全文获取类型
收费全文 | 5146篇 |
免费 | 177篇 |
专业分类
各国政治 | 186篇 |
工人农民 | 231篇 |
世界政治 | 342篇 |
外交国际关系 | 199篇 |
法律 | 3356篇 |
中国政治 | 35篇 |
政治理论 | 947篇 |
综合类 | 27篇 |
出版年
2023年 | 43篇 |
2021年 | 29篇 |
2020年 | 70篇 |
2019年 | 88篇 |
2018年 | 125篇 |
2017年 | 117篇 |
2016年 | 139篇 |
2015年 | 93篇 |
2014年 | 106篇 |
2013年 | 477篇 |
2012年 | 123篇 |
2011年 | 148篇 |
2010年 | 112篇 |
2009年 | 134篇 |
2008年 | 137篇 |
2007年 | 139篇 |
2006年 | 137篇 |
2005年 | 91篇 |
2004年 | 115篇 |
2003年 | 118篇 |
2002年 | 99篇 |
2001年 | 212篇 |
2000年 | 212篇 |
1999年 | 153篇 |
1998年 | 67篇 |
1997年 | 61篇 |
1996年 | 59篇 |
1995年 | 57篇 |
1994年 | 63篇 |
1993年 | 58篇 |
1992年 | 121篇 |
1991年 | 111篇 |
1990年 | 133篇 |
1989年 | 130篇 |
1988年 | 140篇 |
1987年 | 133篇 |
1986年 | 103篇 |
1985年 | 107篇 |
1984年 | 82篇 |
1983年 | 75篇 |
1982年 | 55篇 |
1981年 | 50篇 |
1980年 | 41篇 |
1979年 | 52篇 |
1978年 | 37篇 |
1976年 | 32篇 |
1975年 | 29篇 |
1974年 | 40篇 |
1973年 | 30篇 |
1970年 | 28篇 |
排序方式: 共有5323条查询结果,搜索用时 15 毫秒
211.
The activity of calcium pumping adenosine triphosphatase (Ca2+-ATPase) in cardiac sarcoplasmic reticulum plays a pivotal role in myocardiac contraction-relaxation. The Ca2+-ATPase activity is controlled by phosphorylation and dephosphorylation of a sarcoplasmic reticulum protein "phospholamban" in response to neurotransmitters and drugs. To clarify the role of Ca2+-ATPase in the development of cardiac rigor mortis, we examined the changes of cardiac rigidity and cardiac sarcoplasmic reticulum Ca2+-ATPase activity up to 5 h after the decapitation of rats. Fifteen minutes after decapitation, the rats showed a cardiac rigidity on left ventricles. After 30 min, rigidity was obvious over the whole heart. After 1 h, the rigidity reached a high degree which was maintained for the rest of the observation period. On the other hand, the Ca2+-ATPase activity controlled by phosphorylation and dephosphorylation of phospholamban did not change for the whole observation period (5 h). Another Ca2+-ATPase activity representing the total amount of Ca2+-ATPase in sarcoplasmic reticulum gradually decreased. The data suggest that no significant phosphorylation or dephosphorylation of phospholamban occurs for a short time, at least for 5 h, after death and that the Ca2+-ATPase tends to relax the myocardium against the development of cardiac rigor mortis. 相似文献
212.
T Karlsmark H K Thomsen L Danielsen O Aalund O Nielsen K G Nielsen I K Genefke 《Forensic science international》1988,39(2):175-188
In order to establish pathological evidence in dermis for distinguishing between sequelae of electrical torture and those of other superficial injuries, the skin of eleven fully anaesthetized Danish Landrace pigs have been exposed to heat and electrical energy from either 50 Hz alternating current (a.c.) or direct current (d.c.) via 12 mm large contact knobs or via a pointed 0.5 mm large electrode (only 50 Hz a.c.). The lesions have been examined from 1 to 126 days after the injury. While heat lesions exposed to energy lower than 60 joule only gave minor changes, heat lesions exposed to more than 60 joule showed changes in both collagen fibres (basophilic or eosinophilic fibres without any birefringence or coarse cross-striation in polarized light, respectively) and dermal cells (granular cytoplasm). Areas exposed to 50 Hz a.c. via 0.5 mm. electrode showed basophilic collagen fibres and in a few biopsies on day 7 calcium salts on collagen fibres. Using 12 mm large electrodes the changes were minor, but basophilic and eosinophilic collagen fibres with no birefringence or with fine/coarse cross-striation respectively were seen. Even cells with 'vesicular nuclei' were seen on day 1 and 2 after the injury. The changes in the anode area showed resemblance to that of heat lesions (basophilic collagen fibres). Eosinophilic collagen fibres with fine densely spaced cross-striation in polarized light and 'vesicular nuclei' as well as collagen fibres with calcium salts were seen in the cathode lesions. It is concluded that the dermal changes in the cathode area are specific for electrical injury from day 1 to 14. However, earlier studies have demonstrated dermal changes specific for electrical injury at day 0 and the presence of calcified collagen fibres up to 2 months after injury. The dermal changes in anode lesions were non specific and could not be differentiated from those found in heat lesions. Alternating current lesions (50 Hz) were specific from day 1 to day 7, when the pointed electrode was used, but only in a few days when the energy was transferred via the 12-mm electrodes. 相似文献
213.
Malaysians firms have made inroads into the non-traditional export markets. Such ventures are expected to result in increased knowledge about the marketing systems that are posited to be different from the traditional export markets. This paper reports on the perceived improvement in marketing competencies of Malaysian exporters. The results of data analysis show that there are five dimensions of marketing competency. In ranking order, segmenting and targeting competency is ranked highest followed by product management, export management, product differentiation and promotion. Multiple regression analysis was performed to test the explanatory power of each marketing competency on export performance of firms exporting to China and ASEAN countries. The result revealed that none of the marketing competency explained the variation in export performance for the China market. However, among exporters in ASEAN countries, it was noted that promotion competency resulted in a negative impact on both measures of export performance. Product competency is positively associated with financial measure of export performance. Competencies in segmenting and targeting, and export management are positively associated with non-financial performance. 相似文献
214.
Michael J. Cleveland Mark E. Feinberg Mark T. Greenberg 《Journal of youth and adolescence》2010,39(2):114-126
This study used data from a sample of 6th to 12th grade students (N = 48,641, 51% female), nested in 192 schools, to determine if the influence of family-based protective factors varied across
different school contexts. Hierarchical logistic regression models were used to examine the effects of individual-level family
protective factors, relative to school-level aggregates of the same factors, on recent (past 30 days) use of cigarettes, alcohol,
and marijuana. Cross-level interactions indicated that the effect of the student’s level of family protection, relative to
other students in their school, differed depending on the aggregated school level of family protection. The results suggested
that the benefit of belonging to a well-functioning family was more influential for students attending schools characterized
by higher-than-average aggregated levels of protection compared to students attending schools of lower-than-average protection.
Thus, family-level factors offered less protection for students in relatively high-risk school contexts. These results were
consistent with a protective–reactive interaction and suggest that a thorough understanding of adolescent substance use must
consider the complex interplay among adolescents, their families, and their social environments. 相似文献
215.
Tobias Jung Tim Scott Huw T. O. Davies Peter Bower Diane Whalley Rosalind McNally Russell Mannion 《Public administration review》2009,69(6):1087-1096
Organizational culture is widely considered to be one of the most significant factors in reforming and modernizing public administration and service delivery. This article documents the findings of a literature review of existing qualitative and quantitative instruments for the exploration of organizational culture. Seventy instruments are identified, of which 48 could be submitted to psychometric assessment. The majority of these are at a preliminary stage of development. The study's conclusion is that there is no ideal instrument for cultural exploration. The degree to which any measure is seen as "fit for purpose" depends on the particular reason for which it is to be used and the context within which it is to be applied. 相似文献
216.
Thomas T. Holyoke Jeffrey R. Henig Heath Brown Natalie Lacireno-Paquet 《Policy Sciences》2009,42(1):33-55
Baumgartner and Jones (1993) showed how radically new policies emerge on government agendas as a consequence of exogenous shocks to policy subsystems displacing privileged interests. But how do these policies evolve post-punctuation? In this paper, we present three different models of policy change. Policies may revert to the old status quo if displaced interests re-assert themselves, or they may be “locked-in” by new interests now reaping the benefits. Alternatively, they may incrementally change as lawmakers “learn” how to better meet target population needs, particularly by witnessing how other jurisdictions address similar problems. We test these models with data on change in state charter schools laws over time. We find that whether old status quos are overthrow, and the fate of charter policies when they are enacted, is influenced more by competing political interests, especially interest groups, than elite and public perceptions of broad systemic crises. Yet, we also find that changing demands on the state and learning from the successes and failures of neighboring states also play significant roles. 相似文献
217.
We explore how two populations learn to cooperate with each other in the absence of institutional support. Individuals play iterated prisoner's dilemmas with the other population, but learn about successful strategies from their own population. Our agent-based evolutionary models reconfirm that cooperation can emerge rapidly as long as payoffs provide a selective advantage for nice, retaliatory strategies like tit-for-tat, although attainable levels of cooperation are limited by the persistence of nonretaliatory altruists. Learning processes that adopt the current best response strategy do well only when initial conditions are very favorable to cooperation, while more adaptive learning processes can achieve high levels of cooperation under a wider range of initial conditions. When combined with adaptive learning, populations having larger, better connected learning relationships outperform populations with smaller, less connected ones. Clustered relationships can also enhance cooperation, particularly in these smaller, less connected populations. 相似文献
218.
According to the democratic domino theory, increases or decreases in democracy in one country spread and "infect" neighboring countries, increasing or decreasing their democracy in turn. Using spatial econometrics and panel data that cover over 130 countries between 1850 and 2000, this article empirically investigates the democratic domino theory. We find that democratic dominoes do in fact fall as the theory contends. However, these dominoes fall significantly "lighter" than the importance of this model suggests. Countries "catch" only about 11% of the increases or decreases in their average geographic neighbors' increases or decreases in democracy. This finding has potentially important foreign policy implications. The "lightness" with which democratic dominoes fall suggests that even if foreign military intervention aimed at promoting democracy in undemocratic countries succeeds in democratizing these nations, intervention is likely to have only a small effect on democracy in their broader regions. 相似文献
219.
Current explanations of effective voter mobilization strategies maintain that turnout increases only when a potential voter is persuaded to participate through increased social connectedness. The connectedness explanation does not take into account, however, that registered voters, by registering, have already signaled their interest in voting. The theory presented in this article predicts that impersonal, noticeable messages can succeed in increasing the likelihood that a registered voter will turn out by reminding the recipient that Election Day is approaching. Text messaging is examined as an example of an impersonal, noticeable communication to potential voters. A nationwide field experiment (n = 8,053) in the 2006 election finds that text message reminders produce a statistically significant 3.0 percentage point increase in the likelihood of voting. While increasing social connectedness has been shown to positively affect voter turnout, the results of this study, in combination with empirical evidence from prior studies, suggest that connectedness is not a necessary condition for a successful mobilization campaign. For certain voters, a noticeable reminder is sufficient to drive them to the polls. 相似文献
220.
What participation mechanisms connect citizens and city officials? Do they produce valued outcomes? Surveys of elected officials suggest that microlevel mechanisms such as direct citizen contact are more valuable in meeting participation goals than are mechanisms focusing on macrolevel concerns. However, there is a disconnect between perceptions about value and the use of mechanisms. State‐level participation requirements and a city manager have little effect on the value of a mechanism. These findings raise some questions: why are microlevel participation mechanisms favored, why do some mechanisms have value even though respondents have little experience with them, and why is there a misalignment between participatory goals and the mechanisms used? 相似文献