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   205725篇
  免费   13720篇
  国内免费   1530篇
  220975篇
  2021年   929篇
  2018年   12851篇
  2017年   11602篇
  2016年   8738篇
  2015年   2305篇
  2014年   2459篇
  2013年   2986篇
  2012年   7318篇
  2011年   15739篇
  2010年   13907篇
  2009年   10112篇
  2008年   12191篇
  2007年   13705篇
  2006年   2696篇
  2005年   2717篇
  2004年   3089篇
  2003年   3197篇
  2002年   2910篇
  2001年   9922篇
  2000年   9708篇
  1999年   7265篇
  1998年   1654篇
  1997年   1843篇
  1996年   1611篇
  1995年   1437篇
  1994年   1337篇
  1993年   1300篇
  1992年   4840篇
  1991年   4580篇
  1990年   4018篇
  1989年   4032篇
  1988年   3638篇
  1987年   3109篇
  1986年   2784篇
  1985年   2686篇
  1984年   1987篇
  1983年   1748篇
  1982年   1236篇
  1981年   987篇
  1980年   919篇
  1979年   1765篇
  1978年   1362篇
  1977年   1200篇
  1976年   1031篇
  1975年   1156篇
  1974年   1166篇
  1973年   1164篇
  1972年   1279篇
  1971年   1229篇
  1970年   827篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
1. Circulating concentrations of iodothyronines, luteinizing hormone(LH), estradiol(E2), progesterone and corticosterone were measured in hens before, during, and after a forced molt induced by fasting. 2. Corticosterone increased at the onset of molt, peaked at the maximal molt and returned to pre- and post-molt levels. LH, E2 and progesterone declined during the molt, and the decline was coincident with the cessation of egg production. 3. Thyroxine(T4), triiodothyronine (T3) and reverse triiodothyronine(rT3) increased during the molt. The increases of T4 and T3 were not abolished even if the forced molt was conducted in mild weather.  相似文献   
102.
103.
104.
Using ethyl methane sulfonate (EMS) treatment of the seeds ofline SGE, a new mutant of pea (Pisum sativum L.) with alterationsin root development was obtained. The mutant phenotype dependson the density of the growth substrate: on sand (a high densitysubstrate) the mutant forms a small compact curly root systemwhereas on vermiculite (a low density substrate) differencesbetween the root systems of the mutant and wild type plantsare less pronounced. Genetic analysis revealed that the mutantcarries a mutation in a new pea gene designedcrt (curly roots).Gene crt has been localized in pea linkage group V. The mutantline named SGEcrt showed increased sensitivity to exogenousauxin and an increased concentration of endogenous indole-3-aceticacid (IAA) in comparison with the wild type line SGE. Copyright2000 Annals of Botany Company Pisum sativum L., root development, garden pea mutant, curly roots, auxin, environmental stimulus response  相似文献   
105.
The celiac disease (CD) is an inflammatory condition characterized by injury to the lining of the small-intestine on exposure to the gluten of wheat, barley and rye. The involvement of gluten in the CD syndrome has been studied in detail in bread wheat, where a set of “toxic” and “immunogenic” peptides has been defined. For wheat diploid species, information on CD epitopes is poor. In the present paper, we have adopted a genomic approach in order to understand the potential CD danger represented by storage proteins in diploid wheat and sequenced a sufficiently large number of cDNA clones related to storage protein genes of Triticum monococcum. Four bona fide toxic peptides and 13 immunogenic peptides were found. All the classes of storage proteins were shown to contain harmful sequences. The major conclusion is that einkorn has the full potential to induce the CD syndrome, as already evident for polyploid wheats. In addition, a complete overview of the storage protein gene arsenal in T. monococcum is provided, including a full-length HMW x-type sequence and two partial HMW y-type sequences. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   
106.
Membrane-bound and secreted IgA contain structurally different alpha-chains   总被引:3,自引:0,他引:3  
Three different forms of alpha-chains are synthesized by BF0.3 and 615.2, two cloned cell lines derived from the murine B lymphoma 1.29. The three forms of alpha-chains differ in size, pI, cellular location, and rate of turnover. They were identified by means of lactoperoxidase-catalyzed radioiodination, internal 14C or 35S labeling, and immunofluorescence techniques as membrane-bound(alpha m), secreted (alpha s), and intracellular (alpha ic) proteins. Comparison of immunoglobulin products of the two lymphoma lines with those of a hybridoma cell line, Id 150, which secretes IgA of the 1.29 idiotype but lacks membrane IgA, confirmed the assignments of alpha m, alpha s, and alpha ic. Results of biosynthetic labeling of BF0.3, 615.2, and Id 150 in the presence and absence of tunicamycin suggest that the difference in m.w. and charge observed between alpha m and alpha s can be attributed to differences in primary amino acid structure rather than different degrees of glycosylation.  相似文献   
107.
Toxin gamma is a basic, low-molecular-weight, neurotoxic protein, isolated from the venom of the Brazilian scorpion, Tityus serrulatus. Raman spectra (400-1800 cm-1 region) of this toxin in both the lyophilized state and in 0.1 M acetate buffer (pH 4.5) and the infrared spectrum (700-4000 cm-1 region) of a solid film were investigated. From the vibrational spectra, it can be concluded that the polypeptide backbone of toxin gamma consists of a mixture of the different secondary structures, with predominance of beta-sheet, followed by unordered structure and alpha-helix, with some evidence of beta-turn structures. The four disulfide bridges assume the gauche-gauche-gauche conformation of the CCSSCC fragments. The intensity ratio of the doublet at 853 and 828 cm-1 suggests that four out of the five tyrosine residues are exposed. The three tryptophan residues are exposed on the surface, and the single methionine residue assume the gauche-gauche conformation. Toxin gamma retains full activity in the pH 4.5-7.5 range, but is almost completely inactivated at pH 11.5.  相似文献   
108.
H. Haibach  Y. W. Yesus  J. J. Doggett 《CMAJ》1984,130(9):1165-1166
A 46-year-old man with pentazocine-induced agranulocytosis is described. In previously reported cases of a complete absence of mature neutrophils in the peripheral blood and bone marrow the patients had undergone marrow-depressing treatment with radiation and antineoplastic drugs. This case is unique in that the patient had complete agranulocytosis without predisposing factors.  相似文献   
109.
110.
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