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   224225篇
  免费   15000篇
  国内免费   49篇
  239274篇
  2021年   1776篇
  2018年   3129篇
  2017年   3024篇
  2016年   3673篇
  2015年   3212篇
  2014年   4450篇
  2013年   6331篇
  2012年   7554篇
  2011年   8078篇
  2010年   5734篇
  2009年   4887篇
  2008年   7213篇
  2007年   7491篇
  2006年   7192篇
  2005年   6716篇
  2004年   6862篇
  2003年   6579篇
  2002年   6537篇
  2001年   9284篇
  2000年   8962篇
  1999年   6989篇
  1998年   2128篇
  1997年   1957篇
  1996年   1820篇
  1992年   5474篇
  1991年   5680篇
  1990年   5651篇
  1989年   5621篇
  1988年   5212篇
  1987年   4865篇
  1986年   4444篇
  1985年   4677篇
  1984年   3697篇
  1983年   3026篇
  1982年   2014篇
  1981年   1724篇
  1980年   1725篇
  1979年   3340篇
  1978年   2578篇
  1977年   2378篇
  1976年   2331篇
  1975年   2826篇
  1974年   3118篇
  1973年   3084篇
  1972年   2750篇
  1971年   2605篇
  1970年   2213篇
  1969年   2161篇
  1968年   2032篇
  1967年   1798篇
排序方式: 共有10000条查询结果,搜索用时 7 毫秒
381.
382.
Results are presented from experimental investigations of the angular distributions and energy spectra of fast ions produced in deuterium polyethylene targets under irradiation by picosecond laser pulses with intensities of up to 2 × 1018 W/cm2 in the SOKOL-P facility. The parameters of ion fluxes were measured by time-of-flight spectrometers based on semiconductor detectors.  相似文献   
383.
384.
385.
The effects of a filtering device and an air-line apparatus on breathing pattern were studied in healthy men with different physical characteristics and work capacity. The subjects comprised nine construction workers aged 35-44, and nine firemen aged 21-35. The construction workers' mean maximal oxygen consumption (VO2max) was 34.5 ml min-1 kg-1, the firemen's 66.9 ml min-1 kg-1. Breathing pattern was analyzed for its components, inspiratory time, expiratory time, breathing frequency, tidal volume, and pulmonary ventilation at rest, during two submaximal treadmill walks when the subjects' absolute work load was equal, and during recovery. Neither the filtering device nor the air-line apparatus had a significant effect on breathing pattern when compared with the control values measured twice with a low-resistance breathing valve. A significantly longer expiratory time, lower breathing frequency, and smaller pulmonary ventilation were found for the firemen with the breathing valve and the industrial respirators. The breathing pattern of the construction workers and the firemen differed, but the alterations were not induced by the use of the filtering device or the air-line apparatus when studied at aerobic work levels up to 60% VO2max.  相似文献   
386.
387.
The extended pattern of multiple esterase forms has been revealed in the hemolymph of wax moth Galleria mellonellalarvae infected by the fungi Metarhizium anisopliae, Beauveria bassianaor Paecilomyces fumoso-roseus. The total esterase activity of the hemolymph also increases during mycosis. Mechanical damage of the cuticle, treatment with deltamethrin, and chilling of the caterpillars induced similar changes in the hemolymph pattern of esterase activity. Presumably, the changed spectrum and activity of the hemolymph esterases during mycosis is due to the damaged cuticle and epidermis cells.  相似文献   
388.
A large and increasing number of women in the western world will at some point during their life be investigated morphologically for some type of breast lesion. Fine Needle Aspiration (FNA) is one morphological method which is considered to be the fastest, cheapest and the most patient-friendly approach. However, the frequency of conclusive samples using this method varies and is often too low, especially when performed by unexperienced operators. In this study we have developed and tested a new semi-automated instrument (“CytoTest”) designed for FNA which is intended to improve the efficacy of the technique by increasing the percentage of conclusive samples. A total of 443 consecutive aspiration procedures on palpable breast lesions were performed to compare this new “CytoTest” equipment with the standard protocol using the same type of needles. We conclude that by increasing the extent and frequency of the reciprocatory motions used by an experienced sampling operator as well as enhancing the ejection pressure, the cellular yield can be increased almost three folded compared to the standard protocol. For cases with high amounts of non-diagnostic material (such as blood or cystic fluid) which were discarded, up to four times more sample could be obtained. Furthermore, the frequency of sparse samples under 1 mg was halved with use of the “CytoTest”.  相似文献   
389.
Monoclonal antibodies against regulatory subunit of cAMP-dependent protein kinase, type II, were obtained from pig brain (R II). The immune-affinity sorbent has been synthesized on the basis of monoclonal antibodies against R II. The method was proposed for the purification of homogeneous R II with high cAMP-binding activity using immune-affinity sorbent.  相似文献   
390.
DefattedMadhuca butyraceae seeds contain 24% of crude protein and 10.4% of saponins. The solubility ofMadhuca seed proteins was determined in water and NaCl as a function of pH and minimum solubility occurred at pH 4.0. The proteins consist of three components with S20,w values of 2.2, 9.8 and 15.4. On gel filtration the proteins gave three peaks and on diethylaminoethyl cellulose chromatography they resolved into two components. Thein vitro digestibility ofMadhuca seed protein was found to be 69% when assayed with a pepsin-pancreatin system.  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