全文获取类型
收费全文 | 4412篇 |
免费 | 319篇 |
国内免费 | 2篇 |
专业分类
4733篇 |
出版年
2023年 | 18篇 |
2022年 | 38篇 |
2021年 | 78篇 |
2020年 | 35篇 |
2019年 | 52篇 |
2018年 | 105篇 |
2017年 | 101篇 |
2016年 | 154篇 |
2015年 | 210篇 |
2014年 | 217篇 |
2013年 | 277篇 |
2012年 | 323篇 |
2011年 | 322篇 |
2010年 | 227篇 |
2009年 | 193篇 |
2008年 | 227篇 |
2007年 | 249篇 |
2006年 | 207篇 |
2005年 | 198篇 |
2004年 | 180篇 |
2003年 | 135篇 |
2002年 | 139篇 |
2001年 | 109篇 |
2000年 | 63篇 |
1999年 | 58篇 |
1998年 | 45篇 |
1997年 | 24篇 |
1996年 | 30篇 |
1995年 | 32篇 |
1994年 | 26篇 |
1993年 | 25篇 |
1992年 | 40篇 |
1991年 | 25篇 |
1990年 | 37篇 |
1989年 | 36篇 |
1988年 | 27篇 |
1987年 | 36篇 |
1986年 | 19篇 |
1985年 | 22篇 |
1984年 | 24篇 |
1983年 | 21篇 |
1982年 | 19篇 |
1981年 | 18篇 |
1977年 | 21篇 |
1976年 | 22篇 |
1975年 | 27篇 |
1974年 | 19篇 |
1973年 | 20篇 |
1971年 | 17篇 |
1966年 | 17篇 |
排序方式: 共有4733条查询结果,搜索用时 15 毫秒
11.
C C?té D Tremblay H Riverin P Frémont P A Rogers 《Canadian journal of physiology and pharmacology》1989,67(6):645-649
We tested the effects of inhibiting the carbonic anhydrase activity of rat soleus and extensor digitorum longus muscles on the isometric contractile properties and the resistance to fatigue. SOL and EDL muscles from female rats were incubated in vitro in the presence of methazolamide, a specific inhibitor of carbonic anhydrase, before determining their contractile properties. Methazolamide had no effects on the contractile properties of the soleus muscle (10(-5) or 10(-3) M) and extensor digitorum longus (10(-3) M), except for the half-relaxation time of the soleus muscle which increased significantly. Values for half-relaxation time were significantly increased with both concentrations of the inhibitor. Muscles were then submitted to a fatigue protocol lasting 30 min. During the fatigue test, no significant difference was observed between control and 10(-5) M methazolamide soleus muscles. In presence of 10(-3) M methazolamide however, the soleus muscle showed a significantly increased resistance to fatigue compared with control preparations. No significant effect was observed with the extensor digitorum longus muscle exposed to 10(-3) M methazolamide. Results are discussed in terms of the presence of two different isoforms of carbonic anhydrase that may be associated with calcium uptake and energy metabolic processes, respectively. 相似文献
12.
Marie-Laure Yaspo Nathalie Crété Zoubida Chettouh Jean-Louis Blouin Zohra Rahmani Dominique Stehelin Pierre-Marie Sinet Nicole Créau-Goldberg Jean-Maurice Delabar 《Human genetics》1992,90(4):427-434
To generate new chromosome 21 markers in a region that is critical for the pathogenesis of Down syndrome (D21S55-MX1), we used pulsed field gel electrophoresis (PFGE) to isolate a 600-kb NruI DNA fragment from the WA17 hybrid cell line, which has retained chromosome 21 as the only human material. This fragment, which contains the oncogene ETS2, was used to construct a partial genomic library. Among the 14 unique sequences that were isolated, 3 were polymorphic markers and contained sequences that are conserved in mammals. Five of these markers mapped on the ETS2-containing NruI fragment and allowed us to define an 800-kb high-resolution PFGE map. 相似文献
13.
L P Panchenko O V Egorov I G Skripal' A S Ra?t E M Ivanova V F Zarytova V V Vlasov 《Mikrobiologicheekij zhurnal》1991,53(4):58-63
Stability of alkylating derivatives of decathymidylates protected on the 3'-terminal by cholesterol and phenazine residues has been studied in the process of their interaction with cells of Acholeplasma laidlawii PG-8. It is shown that the studied reagents are not split by nucleases of A. laidlawii PG-8 for the time necessary for alkylation of mycoplasma biopolymers. 相似文献
14.
Data are presented on the aboveground and underground biomass of the speciesMarsilea quadrifolia and on the water regime and soil conditions in a habitat of this species in Central Europe (Czechoslovakia). 相似文献
15.
The purpose of this study was to determine the influence of metabolic stresses, such as endurance training and chronic isoproterenol treatment, on skeletal muscle sensitivity to norepinephrine. Using an isolated perfused rat hindlimb preparation, dose-response curves for skeletal muscle oxygen consumption (VO2) and vascular resistance were obtained with control, endurance trained, and isoproterenol treated rats. No significant difference was found between control and experimental groups for non-stimulated VO2. In response to NE infusion, trained rats showed a significantly greater increase in VO2 compared to control rats while the response of the isoproterenol treated rats was of the same magnitude as the one for their respective control rats. At the highest dose of NE infused, the vasopressor response was significantly lower in trained rats compared to control rats. At none of the doses was there a significant difference in the vasopressor response between control and isoproterenol treated rats. These results suggest that repeated exposures to high levels of catecholamines, as produced during endurance training, leads to an increased sensitivity of skeletal muscle to the effect of norepinephrine. 相似文献
16.
Summary ThreeAlnus glutinosa (L.) Gaertn. clones, obtained byin vitro propagation techniques, were inoculated with four strains ofFrankia. The ability of these clones to nodulate and fix nitrogen was previously reported; this study deals with the performance of 12 different combinations of pairs of symbionts.Shoot fresh weight, shoot height and collar diameter were measured 60 and 82 days after inoculation. Shoot fresh weight seems to be more sensitive and reliable than the other parameters. Nitrogenase activity, measured by the acetylene reduction assay, was assayed 78 days after inoculation and was consistent with the biomass measurements.Better growth was observed when type N strains were used. Significant growth differences were observed between clones AG-2 and AG-8 on the one hand and clone AG-4 on the other. Thus, the use of genetically defined host plants and microsymbionts permitted the demonstration of significant performance variation even among cloned plants from the same provenance (AG-4 and AG-8).The duration of the experiment influenced the results with differences becoming less significant with time. This might be caused by an external limiting factor such as the pot size, competition for light,etc. But it could also be indicative of differences in nodulation speed among the treatments. 相似文献
17.
18.
19.
Widespread mortality of the black sea urchin Diadema antillarum occurred in the Caribbean in 1983; beginning in Panama in January, and having its major impact at Barbados in September. Mortality on ten reefs surveyed in Barbados was 93.2%, with the highest being 99.9% and the lowest 86.9%. Mortality on each reef was independent of the pre-mortality density on the reef. Urchins with test diameters between 20 and 40 mm were more severely affected than smaller or larger urchins. Populations on reefs exposed to incoming oceanic water suffered heavier mortality than those on protected reefs. Mean size of urchins was smallest on high density reefs. This may indicate a negative effect of density on urchin growth. At post-mortality densities, urchins may grow faster and reach sexual maturity sooner. 相似文献
20.
Labuctril 25 (3,5-dibromo-4-hydroxybenzonitrile, LAB) at concentrations up to 100μg/mL inhibits effectively growth, morphology, and pigmentation of most soil streptomycete isolates grown under laboratory conditions. Oxytril CM (OXT), Basagran (BAS) and Faneron 50 WP (FAN) applied at the same concentrations had no detectable effect on growth of substrate mycelium but suppressed both aerial mycelium and pigment formation, the effectivity decreasing in the order OXT—BAS—FAN. The LAB-sensitivity of mutant strains was markedly higher as compared with that of the soil isolates. A wild strain resistant to 100–400μg of LAB per mL (depending on the medium composition) was isolated. It was capable of supporting the growth and development of sensitive strains on the LAB-containing medium. A stimulatory effect of low doses of LAB (10–20μg/mL) on the antibiotic activity of streptomycetes was observed. 相似文献