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   1651653篇
  免费   157213篇
  国内免费   1560篇
  2021年   18226篇
  2019年   16309篇
  2018年   19495篇
  2017年   18276篇
  2016年   29545篇
  2015年   43465篇
  2014年   51544篇
  2013年   77983篇
  2012年   46605篇
  2011年   37423篇
  2010年   47385篇
  2009年   47644篇
  2008年   34326篇
  2007年   33152篇
  2006年   36241篇
  2005年   37139篇
  2004年   36214篇
  2003年   33355篇
  2002年   31389篇
  2001年   54023篇
  2000年   51811篇
  1999年   46600篇
  1998年   27817篇
  1997年   27779篇
  1996年   26747篇
  1995年   24915篇
  1994年   24602篇
  1993年   23914篇
  1992年   39201篇
  1991年   37227篇
  1990年   35884篇
  1989年   36189篇
  1988年   33210篇
  1987年   31396篇
  1986年   29682篇
  1985年   31159篇
  1984年   28849篇
  1983年   25277篇
  1982年   23574篇
  1981年   22313篇
  1980年   21062篇
  1979年   25066篇
  1978年   22223篇
  1977年   20971篇
  1976年   19732篇
  1975年   19909篇
  1974年   20740篇
  1973年   20951篇
  1972年   18171篇
  1971年   16443篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
911.
912.
This paper describes the scale-up from 0.1 to 100 liter of the unit process based on 3-mm-diameter glass spheres for the growth of BHK monolayer cells. The production of four strains of FMD virus at the 0.1-, 10-, and 100-liter scales was examined. Cell growth was estimated from measurements of the concentration of glucose in the growth medium, while the release of virus was inferred from measuring the concentration of LDH in the culture supernatant fluid. The yields of virus at 0.1-, 1-, and 10-liter scales were similar but that from the 100-liter version was somewhat lower. The reason for this lower yield and the method used to overcome it over outlined.  相似文献   
913.
The existence of mechanical noise (MN) has been demonstrated in isolated papillary muscles of rats at rest. The mean amplitude of the MN was about 1 mg, the mean frequency 1.5 Hz (t 22 degrees C). A good agreement was found between the MN amplitude and the contracture level of the muscle. However, during long contractures, the correlation between the noise and contracture magnitude was disturbed. There was no relationship between the MN amplitude and contracture magnitude during exposures inducing metabolic alterations (hypoxia, NaCN) and upsetting the work of the sarcoplasmic reticulum (caffeine). It is believed that the MN amplitude is in a good agreement with the contracture magnitude and, therefore, with the concentration of intracellular Ca2+, if the sarcoplasmic reticulum and contractile elements of the cells are intact.  相似文献   
914.
Morphological taxonomy of simple Hyphomycetes is complicated by the frequent occurrence of pleoanamorphism. In some groups of yeast-like fungi, uncommon synanamorphs are diagnostic. Differences in conidiogenesis do not always delimit natural groups. Some nomenclatural problems are mentioned, with an emphasis on the need of neotypification. Prospects are sketched for future taxonomic research.  相似文献   
915.
In the present study we investigated the binding characteristics of estrogen and antiestrogen-receptor complexes to rabbit uterine chromatin. Activated or nonactivated estrogen receptors were partially purified by DEAE-cellulose chromatography using low (1 mM) or high (10 mM) concentrations of sodium molybdate. Activated [3H]estradiol-receptor complexes showed enhanced binding to chromatin acceptor sites unmasked by 1 M, 4 M and 6 M guanidine hydrochloride. We also examined the chromatin-binding characteristics of the estrogen receptors when bound by the high-affinity triphenylethylene antiestrogen, H1285. The acceptor site activity for the [3H]H1285-receptor complexes was markedly decreased at sites unmasked by 4 M and 6 M guanidine hydrochloride. Further, the nonactivated receptor complexes showed very low binding to deproteinized chromatin. The estrogen-receptor chromatin-acceptor sites were tissue specific and saturable. These chromatin acceptor sites differ in their affinity and capacity (number of binding sites per cell) for the estrogen- and antiestrogen-receptor complexes. Thus, we suggest that the differences in the physiological and physicochemical properties of estrogens and antiestrogens may be related to their differential interaction with uterine chromatin subfractions.  相似文献   
916.
917.
Summary Net aerial primary production and accumulation of nutrients by the grasses and nongrasses of the ground layer community of a cerrado vegetation in central Brazil were determined in burnt and unburnt areas. The net aerial primary production of the ground layer community was 327 gm–2 in the unburnt area and only 242 gm–2 in the burnt area during the first year after fire. Grasses contributed 68 to 78% of the aerial biomass of the ground layer in the unburnt area. The live biomass in the burnt and unburnt areas was comparable by the end of the first dry period after the fire. The major part of N, P and K in the aerial biomass was in the grasses. The concentration of all nutrients in the aerial biomass was generally higher in the burnt area during the first year after the fire.  相似文献   
918.
Three species of blackflies were found in emergence-trap samples taken overa period of 8 months from a second-order, forested, cold-stenothermal stream in southern Ontario. The emergence phenologies of the two common species, Prosimulium mixtum and Stegopterna mutata, are described and compared with their phenologies in other streams in North America. Hypotheses are presented for the poor faunal diversity and prolonged emergence of the two species in the stream studied. Emergence data are used to describe the pupal distribution in the stream.Wing-length measurements showed a distinct dimorphism in P. mixtum: females were larger than males. Adult size (except of P. mixtum females) varied among sampling sites in the stream and, in the case of S. mutata, this variation was time dependent.  相似文献   
919.
A T cell line specific for the chemically well-defined peptidoglycan of bacterial cell wall, disaccharide tetrapeptide, was established from Lewis rats immunized with the antigen covalently linked to the autologous rat serum albumin. The antigen specificity was examined with various analogues or derivatives of the peptidoglycan. The cell line was reactive to analogues with the COOH-terminal D-amino acid, but least reactive to those with L-amino acid as COOH terminus. Transferring of the T cell line into X-irradiated normal Lewis rats induced delayed-type hypersensitivity in an antigen specific manner.  相似文献   
920.
In a radioassay for Vasoactive Intestinal Peptide (VIP)-binding, eight out of 33 plasma samples from healthy human subjects exhibited specific binding ranging from 2.6% to 46.7% of total [125 I]VIP. This binding was competitively displaced by unlabeled VIP. The structurally homologous peptides, Peptide Histidine Isoleucine (PHI) and secretin, were, respectively, 72-fold and 413-fold less potent than VIP in displacing bound [125 I]VIP, whereas the unrelated peptides, neurotensin, eledoisin, bombesin and metenkephalin, were without effect on the binding. The antibody nature of the VIP-binding factor was suggested by its precipitation with ammonium sulfate, attenuation after absorption with Staphylococcus aureus preparations, precipitation with antisera against human IgG and IgM, and coelution with standard IgG and IgM on anion-exchange and high-performance gel-filtration columns. Pepsin treatment of purified IgG fraction yielded a VIP-binding species with apparent molecular weight of 108 +/- 13 kDa that was precipitated by antiserum against the F(ab)2 fragment of the IgG molecule. These results demonstrate the existence in some human plasmas of an autoantibody that binds VIP.  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