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   262196篇
  免费   17804篇
  国内免费   106篇
  280106篇
  2018年   2787篇
  2017年   2693篇
  2016年   3631篇
  2015年   3988篇
  2014年   4965篇
  2013年   7063篇
  2012年   7880篇
  2011年   8640篇
  2010年   5858篇
  2009年   5222篇
  2008年   7436篇
  2007年   7676篇
  2006年   7323篇
  2005年   7009篇
  2004年   6877篇
  2003年   6685篇
  2002年   6552篇
  2001年   12163篇
  2000年   12080篇
  1999年   9331篇
  1998年   2844篇
  1997年   2883篇
  1996年   2817篇
  1995年   2601篇
  1994年   2563篇
  1993年   2459篇
  1992年   7282篇
  1991年   7078篇
  1990年   7140篇
  1989年   6946篇
  1988年   6442篇
  1987年   6099篇
  1986年   5428篇
  1985年   5771篇
  1984年   4571篇
  1983年   3977篇
  1982年   2796篇
  1981年   2604篇
  1980年   2423篇
  1979年   4187篇
  1978年   3193篇
  1977年   2943篇
  1976年   2894篇
  1975年   3331篇
  1974年   3565篇
  1973年   3569篇
  1972年   3102篇
  1971年   2863篇
  1970年   2553篇
  1969年   2323篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Experiments on the transfection of cultured SKOV3 tumor cells of human ovarian adenocarcinoma and HeLa cells of human cervical carcinoma with gene Bax have demonstrated that SKOV3 cells are highly sensitive to the protein product of this gene, whereas the sensitivity of HeLa cells is substantially lower. HeLa cells obtained as a result of Bax transfection and subsequent selection are characterized by an extremely high Bax protein content and a hypersensitivity to doxorubicin. All Bax-transfected SKOV3 cells with an increased Bax content have died. In the SKOV3 cell line, a Bax exon 3 mutation has been found that corresponds to genotype G7/G9, whereas the native type of the Bax gene corresponds to genotype G8/G8. The results suggest that the G7/G9 mutation in Bax exon 3 deprives the Bax protein of proapoptotic activity.Translated from Molekulyarnaya Biologiya, Vol. 39, No. 1, 2005, pp. 40–47.Original Russian Text Copyright © 2005 by Rodina, Sladkova, Obuchova, Vezirkhanova, Moskaleva, Prusakova, Beletskii, Belushkina, Strelnikov, Ivanov, S. Severin, E. Severin.  相似文献   
12.
Contingencies of different components of freshwater biocenoses in the Don, Volga, Angara, and Northern Azov basins where studied by determination analysis. A positive contingency between the biomass of total phytoplankton or its divisions and the biomass of zooplankton was demonstrated. The most significant contingencies were revealed for zooplankton and green algae, dinoflagellates, and cyanobacteria. As against zooplankton, the biomass of zoobenthos features much less contingencies with the biomass of microalgae as well as zooplankton, since detritus, higher plant tissues, and small animals are the basis of the diet of benthic organisms. Differences in the contingency pattern between different geographical regions and time periods within the same basin have been revealed using the context procedure in determination analysis.  相似文献   
13.
Based on the examination and quantitative comparison of the approaches used to assess the energy partitioning in photosystem II, the unified method was proposed to calculate the contribution of the components of nonphotochemical quenching.  相似文献   
14.
Data on cytogenetic examinations of the descendans of Chernobyl disaster liquidators (cleanup personnel) have been obtained. It has been established that the level of spontaneous chromosomal aberrations before folic acid administration was 1.8 times higher than that value after its employment (4.45 vs 2.42%, p < 0.01). In lymphocyte cultures treated with mitomycin C accompanied by folic acid, it was 4.5 times higher before their administration (23.95 vs 5.36%, p < 0.001). The data obtained confirm the possibility of stabilizing the genetic apparatus in the descendans of Chernobyl disaster liquidators after folic acid administration.  相似文献   
15.
16.
The structure of the distribution range and population of the Siberian crane in its regular breeding area in the northeastern Yakutian tundra are described, as well as the migration terms, intensity, routes, and stopover sites. The territorial pairs (71.7–97.1% of the summer population), which in 2006 were represented by the birds at ages of 8 to 21 years (mainly 20 years, accounting for 45.4%), constantly stayed on an area of 7.3–16.5 km2 independently of their participation in breeding. The breeding success in this population varies from 4.3–8.7 to 65.0–83.3% and depends on the climatic conditions at the beginning of egg laying; these climatic conditions change rather unpredictably from year to year, as well as being seasonally unstable. This explains that fact that some generations in this population are particularly vulnerable to natural elimination factors because of their low numbers. Bird migration in Yakutia follows a narrow tunnel with the highest migratory intensity in the Middle Aldan Valley. In the fall, 30 to 50% of the entire population is visually recorded there.  相似文献   
17.
We have designed a flexible ecological momentary assessment/intervention smartphone (EMA/EMI) “app”. We examine the utility of this app for collecting real-time data, and assessing intra-subject variability, by using it to assess how freshman undergraduates spend their time. We also explore whether its use can promote greater self-awareness. Participants were randomly divided into an experimental group, who used the app, and a control group, who did not. We used the app to collect both randomized in-the-moment data as well as end-of-day data to assess time use. Using a posttest survey we asked participants questions about how they spent time throughout the school semester. We also asked the experimental group about their experience with the app. Among other findings, 80.49% participants indicated that they became more aware of how they spent their time using the app. Corroborating this report, among the experimental group, end-of-semester self-assessment of time spent wasted, and time spent using electronics recreationally, predicted semester GPA at a strength comparable to high school GPA and ACT score (two of the best single predictors for first semester college GPA), but had no correlation among controls. We discuss the advantages and limitations of using apps, such as ours, for EMA and/or EMI.  相似文献   
18.
Types of Perceptual Acts: The object of the present study is perceptual acts executed on a static or slowly changing visual information field.  相似文献   
19.
The ranges of two earthworm subspecies, Eisenia nordenskioldi nordenskioldi (Eisen 1879) and E. n. pallida Malevi 1956, differ in area and partially overlap. E. n. nordenskioldi populates the entire Asian Russia and eastern regions of the Russian Plain, from the lower reaches of the Volga and Don rivers to the Arctic Ocean coasts, while E. n. pallida has not expanded to the Asian permafrost zone and does not occur in European Russia and in the Urals. These subspecies “hold the record” in cold hardiness: the worms and cocoons of the nominotypical subspecies withstand temperatures down to ?34 and ?40°C, and those of E. n. pallida, to ?28 and ?23°C, respectively. Hence, their distribution is independent of subzero temperatures, and their ability to overwinter at any phase of the life cycle makes them also independent of heat supply during the summer period. Differences in geographic range may also be due to biological features of the subspecies. The nominotypical subspecies feeds belongs to the epiendogeic morphoecological type (feeding on the ground surface), whereas E. n. pallida is a true endogeic earthworm. Both subspecies have similar requirements for soil acidity; however, conditions in coarse-humus organomineral horizons of frozen soils appear to be unfavorable for E. n. pallida, which accounts for the absence of this subspecies in the permafrost zone.  相似文献   
20.
The effect of the ubiquitous downregulation of insulin receptor (InR) gene expression on the metabolism of juvenile hormone (JH) and dopamine (DA) in young females of D. melanogaster under normal conditions and heat stress is studied. The level of JH degradation and alkaline phosphatase activity (ALP, an enzyme regulating DA synthesis) were used as indicators of JH and DA levels, respectively. We demonstrated that, under normal conditions, the ubiquitous inhibition of the InR gene expression in D. melanogaster females induced an increase in the JH degradation and ALP activity. As we have already shown, this is indicative of the decrease in the concentration of the above hormones. It was also found that the total inactivation of InR does not affect the initiation of JH and DA metabolic system response to heat stress; however, it does affect its intensity. Thus, the involvement of the insulin signaling pathway in the regulation of the JH and DA metabolism in Drosophila females was demonstrated in vivo under normal and stress conditions.  相似文献   
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