首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   4605篇
  免费   426篇
  国内免费   1篇
  2023年   33篇
  2022年   54篇
  2021年   95篇
  2020年   58篇
  2019年   89篇
  2018年   100篇
  2017年   80篇
  2016年   157篇
  2015年   223篇
  2014年   288篇
  2013年   283篇
  2012年   406篇
  2011年   368篇
  2010年   248篇
  2009年   201篇
  2008年   260篇
  2007年   241篇
  2006年   233篇
  2005年   254篇
  2004年   232篇
  2003年   228篇
  2002年   192篇
  2001年   36篇
  2000年   33篇
  1999年   49篇
  1998年   64篇
  1997年   41篇
  1996年   42篇
  1995年   43篇
  1994年   30篇
  1993年   30篇
  1992年   43篇
  1991年   25篇
  1990年   25篇
  1989年   17篇
  1988年   25篇
  1987年   25篇
  1986年   9篇
  1985年   15篇
  1984年   22篇
  1983年   13篇
  1982年   15篇
  1981年   11篇
  1980年   5篇
  1979年   13篇
  1978年   5篇
  1977年   6篇
  1974年   7篇
  1972年   5篇
  1970年   6篇
排序方式: 共有5032条查询结果,搜索用时 726 毫秒
121.
Alison Leitch 《Ethnos》2013,78(4):437-462
This paper explores the emergence of the Slow Food Movement, an international consumer movement dedicated to the protection of ‘endangered foods.’ The history of one of these ‘endangered foods’, lardo di Colonnata, provides the ethnographic window through which I examine Slow Food's cultural politics. The paper seeks to understand the politics of ‘slowness’ within current debates over European identity, critiques of neo-liberal models of rationality, and the significant ideological shift towards market-driven politics in advanced capitalist societies.  相似文献   
122.
We investigate the role of ecology and phylogeny in the association between lizard abundance and microhabitat variables in an Amazon rain forest site. Using pitfall trap arrays, we collected data from 349 individuals belonging to 23 lizard species. After accounting for spatial autocorrelation and using a canonical correspondence analysis (CCA), we found that lizard captures were significantly associated with microhabitat variables, which accounted for 48 percent of the observed variation. Furthermore, a canonical phylogenetic ordination (CPO) indicated that microhabitat variables are more important in determining the distribution of lizard species than phylogenetic relationships among species. Termite nests, canopy openness, and tree circumference were strongly associated with the number of captures of certain lizard species. Our results confirm autecology studies of individual lizard species for which data are available. We suggest that maintaining heterogeneous forested microhabitats should be a central goal for sustaining a high lizard biodiversity in Amazon rain forests.  相似文献   
123.
124.
125.
The mosquito innate immune response is able to clear the majority of Plasmodium parasites. This immune clearance is controlled by a number of regulatory molecules including serine protease inhibitors (serpins). To determine whether such molecules could represent a novel target for a malaria transmission-blocking vaccine, we vaccinated mice with Anopheles gambiae serpin-2. Antibodies against Anopheles gambiae serpin-2 significantly reduced the infection of a heterologous Anopheles species (Anopheles stephensi) by Plasmodium berghei, however this effect was not observed with Plasmodium falciparum. Therefore, this approach of targeting regulatory molecules of the mosquito immune system may represent a novel approach to transmission-blocking malaria vaccines.  相似文献   
126.
The interactions of mouse thymocytes with unilamellar phospholipid vesicles comprised of dimyristyl lecithin (DML), dipalmitoyl lecithin (DPL), dioleoyl lecithin (DOL), and egg yolk lecithin (EYL) were examined in vitro.

In cells treated with [3H]DML or [3H]DPL vesicles, electron microscope (EM) autoradiographic analysis showed most of the radioactive lipids to be confined to the cell surface. Transmission EM studies showed the presence of intact vesicles (DPL) and collapsed or ruptured vesicle fragments (DML) adsorbed to the surfaces of treated cells. In cells treated with DPL vesicles containing a watersoluble dye (6-carboxyfluorescein; 6-CF), most of the fluorescent vesicles were localized at the periphery of the treated cells. Furthermore, substantial fractions of the cell-associated DPL and DML could be released by a mild trypsinization without damaging the cells. These results suggest that the uptake of DML and DPL is primarily due to vesicle-cell adsorption. Such an adsorption process appears to be enhanced at or below the thermotropic-phase transition temperature of the vesicle lipid. Under certain conditions these adherent vesicles also formed patches or caps on the cell surface.

In cells treated with DOL or EYL vesicles, transmission EM and EM autoradiography showed relatively little exogenous vesicle lipid located at the cell surface. Thymocytes incubated (37°C) with [14C] EYL vesicles containing a trapped marker, [3H]inulin, incor porated both isotopes at identical rates. In separate experiments it was found that this marker was located inside the treated cells. Thymocytes treated with DOL vesicles containing 6-CF exhibited a uniform and diffuse distribution of dye in the internal volume of the cells. Little cell-associated EYL or DOL could be released by trypsinization. Evidence against endocytosis of intact vesicles as a major pathway of vesicle uptake is also presented. These observations, coupled with the demonstration of vesicle-cell lipid exchange as a minor component of vesicle uptake suggest that incorporation of EYL and DOL vesicles by thymocytes is primarily by vesicle-cell fusion.  相似文献   
127.
To generate the first series of prodigiosene conjugates, the tripyrrolic skeleton was appended to estrone, tamoxifen and porphyrin frameworks by way of ester linkers and various hydrocarbon chain lengths. The ability of the conjugates to inhibit various types of cancer cells was evaluated in vitro. The porphyrin conjugates did not exhibit significant activity. The estrone conjugates exhibited modest activity, for the most part. However, significantly greater growth inhibition activity against certain breast, colon, lung, leukemia, melanoma and prostate cell lines was noted. This unusual effect for this first generation model class of compound warrants further investigation and comparison to cases where estrogens are linked to prodigiosenes via connection points that do not feature in estrogen receptor binding. The 4-hydroxytamoxifen conjugates exhibit nanomolar range activity against the MCF-7 breast cancer cell line, paving the way to expand the scope and connectivity of prodigiosene–tamoxifen conjugates.  相似文献   
128.
The mechanisms as well the genetics underlying the bioavailability and metabolism of carotenoids in humans remain unclear. To begin to address these questions, we used cluster analysis to examine individual temporal responses of plasma carotenoids from a controlled-diet study of subjects who consumed carotenoid-rich beverages. Treatments, given daily for 3 weeks, were watermelon juice at two levels (20-mg lycopene, 2.5-mg β-carotene, n=23 and 40-mg lycopene, 5-mg β-carotene, n=12) and tomato juice (18-mg lycopene, 0.6-mg β-carotene, n=10). Cluster analysis revealed distinct groups of subjects differing in the temporal response of plasma carotenoids and provided the basis for classifying subjects as strong responders or weak responders for β-carotene, lycopene, phytoene and phytofluene. Individuals who were strong or weak responders for one carotenoid were not necessarily strong or weak responders for another carotenoid. Furthermore, individual responsiveness was associated with genetic variants of the carotenoid metabolizing enzyme β-carotene 15,15'-monooxygenase 1. These results support the concept that individuals absorb or metabolize carotenoids differently across time and suggest that bioavailability of carotenoids may involve specific genetic variants of β-carotene 15,15'-monooxygenase 1.  相似文献   
129.
130.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号