全文获取类型
收费全文 | 26089篇 |
免费 | 2895篇 |
国内免费 | 12篇 |
专业分类
28996篇 |
出版年
2022年 | 183篇 |
2021年 | 366篇 |
2020年 | 221篇 |
2019年 | 262篇 |
2018年 | 321篇 |
2017年 | 301篇 |
2016年 | 517篇 |
2015年 | 916篇 |
2014年 | 944篇 |
2013年 | 1198篇 |
2012年 | 1470篇 |
2011年 | 1469篇 |
2010年 | 1008篇 |
2009年 | 860篇 |
2008年 | 1212篇 |
2007年 | 1255篇 |
2006年 | 1226篇 |
2005年 | 1187篇 |
2004年 | 1106篇 |
2003年 | 1090篇 |
2002年 | 1117篇 |
2001年 | 508篇 |
2000年 | 491篇 |
1999年 | 502篇 |
1998年 | 371篇 |
1997年 | 335篇 |
1996年 | 322篇 |
1995年 | 257篇 |
1994年 | 263篇 |
1993年 | 274篇 |
1992年 | 376篇 |
1991年 | 352篇 |
1990年 | 372篇 |
1989年 | 347篇 |
1988年 | 329篇 |
1987年 | 336篇 |
1986年 | 270篇 |
1985年 | 326篇 |
1984年 | 294篇 |
1983年 | 273篇 |
1982年 | 301篇 |
1981年 | 264篇 |
1980年 | 218篇 |
1979年 | 241篇 |
1978年 | 222篇 |
1977年 | 203篇 |
1976年 | 184篇 |
1974年 | 201篇 |
1973年 | 189篇 |
1971年 | 169篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
Summary The quantitative growth of Pseudococcomyxa adhaerens on glass cover slips in distilled water has been studied. Growth is limited by the supply of inorganic nutrients. Regular replacement of the distilled water gives an increase in the growth rate. The light intensity for maximum growth is a function of the nutrient supply. In a culture solution the rate of growth is about 8 times as great as in distilled water, and the limiting light intensity is increased to 400 lux from 100 lux. 相似文献
132.
133.
J. L. Taylor 《The Australian journal of anthropology》1989,19(2):112-125
This paper is concerned with the ongoing intense interest in Thailand of two controversial urban Buddhist movements which have appeared since the beginning of the seventies, Santi Asok and Thammakaai. Essentially, I view both as a resonance of the perceived need for ‘change’ among an articulate aspiring new middle class. I also argue that both Santi Asok and Thammakaai in their expressions — Thammakaai the specious discursive function of capital, Santi Asok by confrontation and spurning what they consider an ‘amoralistic’ establishment — are predicating a radical critique of the Thai social order, a call for collective ‘inner-worldly activism’ and ‘individualistic’ reflexive response to convention. 相似文献
134.
135.
136.
Cervical cancer screening and demonstration projects to identify barriers to optimal screening are discussed. Interview surveys showed that older women and women in low-income groups tended to have lower rates of Papanicolaou smear screening. Data produced by demonstration projects established by the Centers for Disease Control in collaboration with state and local authorities and private institutions will be used to design and implement strategies for increasing screening levels to further reduce cervical cancer mortality. 相似文献
137.
The differentiation of T Lymphocytes within the thymus is an important biological phenomenon during wich these cell acquire their functions to further control the immune system. Numerous experiments under various conditions have been devised to understand the different mechanisms involved in this complex process. Nevertheless, interpretation of these experiments lead to still contradictory debatable hypotheses. Modelisation of this process through classical simulation methods cannot be envisaged because they are not adapted to modifications of the model structure, which is the point of interest. For these reasons, we proposed a new approach of automatic search for model. The program consists of four independent connected modules : The generator produces model, based on the rationale of formal grammars. Protocol and experimental data are stored in a set of experiments. The simulator using a protocol and a model provides simulated results. Finally, the supervisor by comparing simulated results and experimental data, adapts the model parameters to increase their fit and either chooses a new experiment to explore, or modifies the model structure. Change of the model structure is performed among still unexplored models according to their promise level, which is iteratively evaluated relatively to previously explored models through a proposed model distance. The generator is written in Prolog and the other modules in C++. The architecture of the program allows us to modify or complete a module without changing anything in the other modules. As a consequence, the proposed modeling approach conceived to study T lymphocyte differentiation within the thymus remains independent of this biological phenomenon and can be applied to other biological problems. 相似文献
138.
Twenty-seven adipocyte-specific, cell surface-exposed proteins were detected by derivatizing undifferentiated and differentiated 3T3-L1 cells with membrane impermeant sulfosuccinimidyl 2-(biotinamido)ethyl-1,3-dithiopropionate at 0 degrees C. Biotinylated proteins were adsorbed onto streptavidin-agarose, resolved on two-dimensional polyacrylamide gels, and detected by autoradiography or silver staining. Of the surface-exposed proteins specific to adipocytes, three were phosphorylated and seven were glycoproteins that bound to wheat germ agglutinin and eluted with N-acetylglucosamine. Eleven of the adipocyte-specific proteins were bound to streptavidin-agarose after the cells were biotinylated at 20 degrees C and then stripped with glutathione at 0 degrees C to isolate plasma membrane proteins that localize to recycling endosomes as well as the cell surface. When insulin-deprived cells were acutely treated with insulin, only a few proteins, including one protein tentatively identified as the GLUT4 glucose transporter, were found to increase in concentration at the cell surface. These latter results imply that up-regulation of glucose transport by the translocation of GLUT4 to the cell surface in response to insulin occurs by exocytic fusion of an intracellular compartment having a limited number of proteins. 相似文献
139.
The putative periclinal chimeraRhododendron xlimbatum President Roosevelt was used to study the origin of shoots in vitro. Genotypic segregation readily occurred in vitro. Numerous phenotypes were observed, although most shoots were either entirely green or maintained the original variegation pattern. Derivatives of the third apical layer were rarely involved in shoot formation. A reversed chimeral form was isolated. Adventitious shoots were usually miniaturized and rapidly proliferating, but axillary shoots had thicker stems, larger leaves and proliferated more slowly. Corolla tissue produced stunted, leafy shoots; no variegated shoots were produced from floret explants. In shoot tip cultures the addition of 40M 2iP without IBA resulted in the greatest number of shoots. Explant choice was the most critical factor for maintenance of foliar variegation. 相似文献
140.
Bruce C. Tilley Janise L. Meyertons Mary P. Lechevalier 《Journal of industrial microbiology & biotechnology》1990,5(5):329-332
Summary A previously undescribed cryptic phage was found associated withMicromonospora purpurea ATCC 15835. 相似文献