全文获取类型
收费全文 | 8825篇 |
免费 | 813篇 |
国内免费 | 3篇 |
出版年
2023年 | 70篇 |
2022年 | 144篇 |
2021年 | 298篇 |
2020年 | 165篇 |
2019年 | 241篇 |
2018年 | 202篇 |
2017年 | 215篇 |
2016年 | 336篇 |
2015年 | 580篇 |
2014年 | 623篇 |
2013年 | 683篇 |
2012年 | 861篇 |
2011年 | 782篇 |
2010年 | 463篇 |
2009年 | 394篇 |
2008年 | 533篇 |
2007年 | 458篇 |
2006年 | 420篇 |
2005年 | 386篇 |
2004年 | 329篇 |
2003年 | 255篇 |
2002年 | 218篇 |
2001年 | 109篇 |
2000年 | 91篇 |
1999年 | 79篇 |
1998年 | 35篇 |
1997年 | 30篇 |
1996年 | 40篇 |
1995年 | 35篇 |
1994年 | 32篇 |
1993年 | 23篇 |
1992年 | 58篇 |
1991年 | 48篇 |
1990年 | 26篇 |
1989年 | 26篇 |
1988年 | 30篇 |
1987年 | 28篇 |
1986年 | 22篇 |
1985年 | 26篇 |
1984年 | 25篇 |
1983年 | 21篇 |
1982年 | 13篇 |
1981年 | 12篇 |
1979年 | 13篇 |
1977年 | 19篇 |
1976年 | 19篇 |
1974年 | 26篇 |
1973年 | 13篇 |
1972年 | 13篇 |
1970年 | 10篇 |
排序方式: 共有9641条查询结果,搜索用时 599 毫秒
91.
The concentration of VIP was measured radioimmunochemically in cerebrospinal fluid (CSF) from 14 healthy volunteers and from 22 patients with multiple sclerosis. Significantly lower levels of VIP was obtained in the patients (18 +/- 3 pmol/l) than in controls (37 +/- 4 pmol/l). There was no correlation between the level of VIP in CSF and other CSF parameters such as albumin. IgG or cell content; nor between VIP concentration and the physical handicap or neuropsychiatric symptoms. There was a trend towards lower values of VIP in patients with steadily progressing rather than intermittent course of the disease but the difference between the groups was not significant. 相似文献
92.
93.
Anthers of different species of the genera Anemone, Clematis, Papaver and Nicotiana were cultured by floating on a liquid medium which overlay an agarified charcoal medium . This technique proved to be superior to conventional methods i.e. culture on either solid or liquid media. Cold treatment of Anemone anthers for 7 days after inoculation on the double layer medium gave about the same frequency of embryos per anther as corresponding cultures cold treated before inoculation. An elevation of the CO2 concentration to 2% stimulated embryogenesis in anther cultures of Anemone canadensis, Anemone vitifolia, Papaver setigerum and Papaver radicatum . Cold treatment of cultures of Anemone canadensis inhibited embryogenesis if the ensuing culture was performed in 2% CO2. On the other hand, cold treatment was stimulating, with an optimum of about 20 days, if the cultures were maintained in normal air. Chemical analysis of untreated anthers of Anemone canadensis showed the presence of abscisic acid (2.2 × 10−6 g/g anthers). Cold treatment reduced the concentration of abscisic acid to 0.6 × 10−6 g/g anthers. By use of assays with Lemna gibba as test organism, activated charcoal was shown to adsorb abscisic acid that was added to the medium. Medium treated with charcoal before inoculation of anthers of Anemone canadensis provided to inhibit embryo production. 相似文献
94.
125I-labelled fibronectin is shown to bind to both native and denatured collagen immobilized on Sephadex beads in reactions that exhibit different kinetics. The rates of both reactions were enhanced by the presence of heparin or highly sulphated dextran sulphate but not by other glycosaminoglycans or dextran sulphates having low sulphate contents. 相似文献
95.
HVA and 5-HIAA in human cerebrospinal fluid were quantitatively determined by both fluorometry and mass fragmentography. The homovanillic acid values obtained by fluorometry were significantly lower than those obtained by mass fragmentography (P < 0.05). The correlation coefficient between values for HVA obtained by the two methods was high, r= 0.90. For 5-HIAA the concentrations obtained by the two methods were not significantly different while the correlation coefficient was lower, r= 0.55. 相似文献
96.
Peripheral blood lymphocytes from 43 patients with Hodgkin's disease were studied for spontaneous growth in longterm cultures in vitro. The rate of culture establishment in Hodgkin's patients was dependant on a positive Epstein-Barr-Virus (EBV)-seroreactivity and intact delayed hypersensitivity reaction to tuberculin. Localized and inactive disease, as well as the absence of atypical mononuclear cells in the peripheral blood had a favourable influence on the longterm in vitro growth. The overall establishment rate in Hodgkin patients was 18 out of 60 attempts (30%), 16 out of 34 (47%) in patients without treatment, only 2 out of 26 (7.7%) attempts during treatment. These results were compared with culture attempts of peripheral blood cells from healthy individuals and umbilical cord blood lymphocytes. Only 12 out of 60 attempts in healthy donors (18.2%) and 0 out of 49 attempts with umbilical cord blood lymphocytes were successful. 相似文献
97.
98.
Copper toxicosis of Bedlington Terriers (Chronic progressive hepatitis) is a genetically transmitted disease. The typical feature of this disease is accumulation of copper in the liver tissue. The changes vary from mild hepatitis to chronic progressive hepatitis and cirrhosis. The material of this study consists of 2 cases of copper toxicosis examined at the Department of Pathology in Helsinki in the years 1980–82. Moreover a re-examination of tissue samples was made of all Bedlington Terriers examined during the years 1969–1982 at the same department. Six of the 14 examined dogs showed a positive reaction for copper in their liver tissues. The possible relationship of the examined dogs is not yet known. 相似文献
99.
D P Wilcox E Chang K L Dickson K R Johansson 《Applied and environmental microbiology》1983,46(2):406-416
The microbial dynamics associated with granular activated carbon (GAC) in a pilot water treatment plant were investigated over a period of 16 months. Microbial populations were monitored in the influent and effluent waters and on the GAC particles by means of total plate counts and ATP assays. Microbial populations between the influent and effluent waters of the GAC columns generally increased, indicating microbial growth. The dominant genera of microorganisms isolated from interstitial waters and GAC particles were Achromobacter, Acinetobacter, Aeromonas, Alcaligenes, Bacillus, Chromobacterium, Corynebacterium, Micrococcus, Microcyclus, Paracoccus, and Pseudomonas. Coliform bacteria were found in small numbers in the effluents from some of the GAC columns in the later months of the study. Oxidation of influent waters with ozone and maintenance of aerobic conditions on the GAC columns failed to appreciably enhance the microbial growth on GAC. 相似文献
100.
L Strandberg D A Lawrence L B Johansson T Ny 《The Journal of biological chemistry》1991,266(21):13852-13858
Plasminogen activator inhibitor 1 (PAI-1) is sensitive to oxidative inactivation, and it has been suggested that specific oxidation of a methionine residue, Met347, situated in the P1' position of the reactive center may be the cause of the inactivation. To test this hypothesis we have purified and biochemically characterized mutant proteins of PAI-1 in which Met347 and either of two other methionines, Met266 or Met354, has been replaced with oxidation-resistant valine residues. The mutant proteins were found to be equally sensitive to oxidation as wild-type PAI-1, suggesting that a specific oxidation of the P1' Met347 is not responsible for the inactivation. When PAI-1 was oxidized, circular dichroism analysis revealed a rapid conformational change that correlated to the loss of inhibitory activity. The oxidation sensitivity of PAI-1 was enhanced dramatically in the presence of 0.001% sodium dodecyl sulfate, and the circular dichroism spectrum was significantly different from that of untreated PAI-1, suggesting that the increased sensitivity to oxidation may be caused by a conformational change in the inhibitor molecule. Taken together, our data suggest that the oxidative inactivation of PAI-1 is not caused by the specific oxidation of the P1' methionine but results from a conformational change in the protein structure. 相似文献