全文获取类型
收费全文 | 421442篇 |
免费 | 47480篇 |
国内免费 | 179篇 |
出版年
2018年 | 3906篇 |
2017年 | 3805篇 |
2016年 | 5271篇 |
2015年 | 7214篇 |
2014年 | 8291篇 |
2013年 | 12037篇 |
2012年 | 13575篇 |
2011年 | 13564篇 |
2010年 | 9034篇 |
2009年 | 8362篇 |
2008年 | 12051篇 |
2007年 | 12188篇 |
2006年 | 11670篇 |
2005年 | 10997篇 |
2004年 | 10855篇 |
2003年 | 10410篇 |
2002年 | 10147篇 |
2001年 | 18997篇 |
2000年 | 19170篇 |
1999年 | 15596篇 |
1998年 | 5546篇 |
1997年 | 5773篇 |
1996年 | 5590篇 |
1995年 | 5062篇 |
1994年 | 5175篇 |
1993年 | 5023篇 |
1992年 | 12964篇 |
1991年 | 12374篇 |
1990年 | 12308篇 |
1989年 | 12280篇 |
1988年 | 11178篇 |
1987年 | 10625篇 |
1986年 | 9842篇 |
1985年 | 9894篇 |
1984年 | 8023篇 |
1983年 | 6981篇 |
1982年 | 5315篇 |
1981年 | 4685篇 |
1980年 | 4573篇 |
1979年 | 7684篇 |
1978年 | 5943篇 |
1977年 | 5302篇 |
1976年 | 5134篇 |
1975年 | 5540篇 |
1974年 | 5795篇 |
1973年 | 5712篇 |
1972年 | 5172篇 |
1971年 | 4567篇 |
1970年 | 4041篇 |
1969年 | 3741篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
221.
222.
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
223.
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
224.
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
225.
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
226.
Summary A major chromosomal abnormality was observed in 10.3% of subfertile men in this study. This result is similar to a previous survey using the same criteria for selection of probands. The high frequency of chromosomal abnormalities emphasizes the importance of cytogenetic examination in subfertile men. The detection of such an abnormality should be followed by chromosome analysis in the patient's family. Prenatal diagnosis is indicated if a subfertile man with an abnormal karyotype fathers a child. 相似文献
227.
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
228.
229.
Progesterone metabolism in T47Dco human breast cancer cells--II. Intracellular metabolic path of progesterone and synthetic progestins 总被引:1,自引:0,他引:1
K B Horwitz A W Pike C Gonzalez-Aller P V Fennessey 《Journal of steroid biochemistry》1986,25(6):911-916
We show here that progesterone added to the medium of proliferating T47Dco human breast cancer cells is metabolized with a half life of 2-4h. The final metabolic product, 5 alpha-pregnan-3 beta,6 alpha-diol-20-one, (P-metabolite) is released into the medium. This structure suggested that the intracellular metabolism of progesterone involves the enzymes 5 alpha-reductase, 3 beta-hydroxysteroid dehydrogenase, and 6 alpha-hydroxylase. To investigate this pathway, the cells were incubated with a variety of potential substrates. In addition to progesterone, only precursors with the 5 alpha-configuration served as substrates for the enzymes leading to P-metabolite formation. Some precursors with a 5 beta-configuration were also metabolized by T47Dco cells. This metabolism reflected activity by either 3 beta-hydroxysteroid dehydrogenase and/or 6 alpha-hydroxylase but, in contrast to progesterone metabolism, the rates were different and the products were often mixtures. In T47Dco and MCF-7 human breast tumor cells, the reduction at C-3 followed by 6 alpha-hydroxylation, appear to be the major, and possibly only, route of progesterone metabolism. In contrast, preliminary data suggest that in normal human breast epithelial cells, this is not an exclusive route. Androgens are partially subject to the same metabolic enzymes, but synthetic progestins are not metabolized by T47Dco during an 18 h incubation. 相似文献
230.