全文获取类型
收费全文 | 601694篇 |
免费 | 61166篇 |
国内免费 | 381篇 |
出版年
2018年 | 6043篇 |
2017年 | 6060篇 |
2016年 | 9416篇 |
2015年 | 14027篇 |
2014年 | 15390篇 |
2013年 | 19930篇 |
2012年 | 21007篇 |
2011年 | 19019篇 |
2010年 | 13429篇 |
2009年 | 12491篇 |
2008年 | 15563篇 |
2007年 | 16075篇 |
2006年 | 15082篇 |
2005年 | 20133篇 |
2004年 | 18762篇 |
2003年 | 16480篇 |
2002年 | 13757篇 |
2001年 | 29100篇 |
2000年 | 28447篇 |
1999年 | 22955篇 |
1998年 | 6981篇 |
1997年 | 7411篇 |
1996年 | 6808篇 |
1995年 | 6338篇 |
1994年 | 6100篇 |
1993年 | 6040篇 |
1992年 | 18406篇 |
1991年 | 17722篇 |
1990年 | 17218篇 |
1989年 | 16715篇 |
1988年 | 15393篇 |
1987年 | 14300篇 |
1986年 | 13254篇 |
1985年 | 13075篇 |
1984年 | 10493篇 |
1983年 | 8725篇 |
1982年 | 6344篇 |
1981年 | 5712篇 |
1980年 | 5380篇 |
1979年 | 9792篇 |
1978年 | 7413篇 |
1977年 | 6758篇 |
1976年 | 6148篇 |
1975年 | 6914篇 |
1974年 | 7562篇 |
1973年 | 7356篇 |
1972年 | 6731篇 |
1971年 | 6190篇 |
1970年 | 5342篇 |
1969年 | 5114篇 |
排序方式: 共有10000条查询结果,搜索用时 625 毫秒
321.
Raj K. Singh Mary F. Ruh Thomas S. Ruh 《Biochimica et Biophysica Acta (BBA)/General Subjects》1984,800(1):33-40
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
322.
323.
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
324.
Induction of delayed-type hypersensitivity by the T cell line specific to bacterial peptidoglycans 总被引:1,自引:0,他引:1
M Katsuki K Kakimoto S Kawata S Kotani T Koga 《Journal of immunology (Baltimore, Md. : 1950)》1987,139(11):3570-3572
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
325.
S Paul P Heinz-Erian S I Said 《Biochemical and biophysical research communications》1985,130(1):479-485
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
326.
327.
The effect of UV light (lambda = 254 nm) on calf thymus DNP at low ionic strengths was studied. It was found that at the irradiation doses used the protein in the DNA-protein complex increases as the irradiation dose rises. Thermal treatment and acid hydrolysis resulted in a predominant release of histones H3 and H1 from the complex. Data from liquid high performance chromatography, amino acid analysis, thin-layer chromatography point to the induction by UV-light of a thymine-lysine bond, whose formation involves DNA thymines and histone lysine residues, predominantly H3 and H1 fractions. 相似文献
328.
Using two-dimensional thin-layer chromatography, the effect of serotonin on the yield of thymine dimers and on cleavage of the N-glycosidic bond in the DNA irradiated with ultraviolet (UV) light and X-ray was studied. Bound serotonin was shown to reduce the synthesis of UV-induced thymine dimers but had no effect on the number of X-ray-induced breaks in the N-glycoside bonds in thymidine residues. The data obtained are discussed in terms of the mechanisms of serotonin involvement in the photoprotection of yeast cells from the lethal action of UV and X-ray irradiations. 相似文献
329.
The dynamics of leucocytes in abdominal abscesses were studied using indium-111 autologous leucocyte scanning in 30 patients. Thirteen patients showing enteric drainage of leucocytes on delayed scans were characterised by a lack of abdominal localising signs and a low detection rate by ultrasound (25%). By contrast, 16 of 17 patients without enteric drainage had abdominal signs, and in these patients ultrasound was associated with a higher detection rate (58%). Despite the presence of an enteric route of drainage for the abscess 10 of the 13 patients needed surgical intervention. These results help explain the wide variation in clinical presentation of abdominal abscesses; suggest that 111In leucocyte scanning should be the initial investigation in those patients without focal signs; and show that formal surgical drainage is needed in patients recognised as having enteric communication with abscesses. 相似文献
330.