全文获取类型
收费全文 | 13240篇 |
免费 | 1152篇 |
国内免费 | 94篇 |
出版年
2022年 | 169篇 |
2021年 | 270篇 |
2020年 | 166篇 |
2019年 | 199篇 |
2018年 | 243篇 |
2017年 | 226篇 |
2016年 | 403篇 |
2015年 | 647篇 |
2014年 | 647篇 |
2013年 | 834篇 |
2012年 | 1047篇 |
2011年 | 977篇 |
2010年 | 606篇 |
2009年 | 533篇 |
2008年 | 745篇 |
2007年 | 716篇 |
2006年 | 689篇 |
2005年 | 621篇 |
2004年 | 539篇 |
2003年 | 496篇 |
2002年 | 450篇 |
2001年 | 277篇 |
2000年 | 250篇 |
1999年 | 220篇 |
1998年 | 142篇 |
1997年 | 83篇 |
1996年 | 106篇 |
1995年 | 102篇 |
1994年 | 69篇 |
1993年 | 98篇 |
1992年 | 150篇 |
1991年 | 117篇 |
1990年 | 115篇 |
1989年 | 116篇 |
1988年 | 89篇 |
1987年 | 104篇 |
1986年 | 103篇 |
1985年 | 106篇 |
1984年 | 76篇 |
1983年 | 77篇 |
1982年 | 64篇 |
1981年 | 66篇 |
1980年 | 63篇 |
1979年 | 83篇 |
1978年 | 67篇 |
1977年 | 55篇 |
1976年 | 59篇 |
1975年 | 52篇 |
1974年 | 53篇 |
1973年 | 51篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
21.
The initial time of synthesis of globin polypeptide chains in differentiating red cells has been delineated. Three analytical techniques were used, namely, SDS-polyacrylamide gel electrophoresis, acid urea polyacrylamide gel electrophoresis, and two-dimensional gel electrophoresis. The results indicate that globin peptide chains are synthesized in proerythroblasts at the initial time when globin mRNA first enters into the cytoplasm, and there is no apparent time gap between these two events. 相似文献
22.
A case is presented of toxic shock syndrome in a patient with systemic lupus erythematosus. Toxic shock syndrome is rarely reported in patients who are immunosuppressed, perhaps because such patients are often treated vigorously with antibiotics at the earliest sign of infection. The association in this case may have been coincidental. 相似文献
23.
Studies on the synthesis and secretion of the sex-dependent urinary protein, alpha2mu-globulin, have been extended by establishing its sequential passage from the rough to the smooth endoplasmic reticulum and Golgi-rich fractions of the liver of adult male rats. After injection of 14C-labeled amino acids, the maximum radioactivity of alpha2mu occurred at 20 min in the rough, 25 min in the smooth microsomes and 30 or 35 min in the Golgi-rich fractions. Radioactive alpha2mu-globulin appeared in the bloodstream and kidneys after a lag of 20--25 min. Results indicate that alpha2mu-globulin follows a secretory pathway similar to that of serum albumin. 相似文献
24.
From 1974 to 1989, a total of 24,500 aborigines at 67 villages in ten mountainous districts/towns in Taiwan were examined for the Taiwan Taenia infection and 12% were found to be infected. In order to define the clinical manifestations of taeniasis caused by the Taiwan Taenia, 1661 aborigines in ten mountainous districts were surveyed. The overall clinical rate was 76%. The clinical rate was highest among Atayal aborigines (81%), followed by Bunun (66%) and Yami (61%) aborgines and lowest among Ami aborigines (40%). Among 1153 infected people, 10% had passed gravid segments in the faeces for less than 1 year, 24% for 1-3 years, 17% for 4-5 years, 23% for 6-10 years, 16% for 11-20 years, 7% for 21-30 years, and 3% over 30 years. Twenty-six occurrences of gastrointestinal and neurological symptoms were reported by 1258 infected persons. Passing proglottides in the faeces (95%) was the most frequent sign, followed by pruritis ani (77%), nausea (46%), abdominal pain (45%), dizziness (42%), increased appetite (30%), headache (26%), etc. 相似文献
25.
John W. Y. Chan Ronald S. Burton 《Evolution; international journal of organic evolution》1992,46(3):721-734
Flooding results in induction of anaerobic metabolism in many higher plants. As an important component of anaerobic energy production, alcohol dehydrogenase (ADH) activity increases markedly in response to flooding in white clover, Trifolium repens. Significant inter-individual variation in flood-induced ADH activity exists in natural populations of T. repens. The genetic basis of this variation was analyzed by offspring-midparent regression of data from 75 greenhouse reared families; the estimated heritability of flood-induced ADH activity was 0.55 (±0.13). Genetic variation in flood-induced ADH activity has pronounced effects on physiological response and flood tolerance in this species. ADH activity is positively correlated with the rate of ethanol production, indicating that observed in vitro activity differences are manifested in in vivo physiological function. T. repens plants with higher ADH activities during flooding have greater flood tolerance (measured as growth rate when flooded/unflooded growth rate). Variation in ADH activity during flooding accounts for more than 79% of the variance in flood tolerance. On the basis of a limited field survey of populations occupying three sites differing in exposure to flooding conditions, individuals from site C, the most frequently flooded site, expressed significantly higher average ADH activity when flooded than individuals from site A, a site with no history of flooding. Since ADH activity levels are not correlated with electrophoretic mobility variation in T. repens, this work supports previous suggestions that regulatory variation in enzyme activity may play a central role in biochemical adaptations to environmental stress. 相似文献
26.
27.
The nerve growth factor: Thirty-five years later 总被引:15,自引:0,他引:15
Rita Levi-Montalcini 《Bioscience reports》1987,7(9):681-699
28.
Big Moose Basin: simulation of response to acidic deposition 总被引:2,自引:1,他引:1
George F. Davis John J. Whipple Steven A. Gherini Carl W. Chen Robert A. Goldstein Arland H. Johannes Peter W.H Chan Ronald K. Munson 《Biogeochemistry》1987,3(1-3):141-161
The ILWAS model has been enhanced for application to multiple-lake hydrologic basins. This version of the model has been applied to the Big Moose basin, which includes Big Moose Lake and its tributary streams, lakes, and watersheds. The basin, as defined, includes an area of 96 km2, with over 20 lakes and ponds, and 70 km of streams. Hydrologic and chemical calibrations have been made using data from seven sampling stations. When total atmospheric sulfur loading to the basin is halved, the model predicts, after four years of simulation, a decreasing sulfate concentration and to a lesser extent a rising alkalinity at Big Moose Lake outlet. At the end of four years, the results show an increase in pH of 0.1 to 0.5 pH units depending upon season. 相似文献
29.
Stephen Chan James Orenberg Noam Lahav 《Origins of life and evolution of the biosphere》1987,17(2):121-134
The adsorption of 5-AMP and 5-CMP was studied in saturated solutions of several soluble mineral salts (NaCl, Na2SO4, MgCl2·6H2O, MgSO4·7H2O, CaCl2·2H2O, CaSO4·2H2O, SrCl2·6H2O, SrSO4, and ZnSO4·7H2O) as a function of pH, ionic strength, and surface area of the solid salt. The adsorption shows a pH dependence; this can be correlated with the charge on the nucleotide molecule which is determined by the state of protonation of the N-1 nitrogen of 5-AMP or N-3 nitrogen of 5-CMP and the phosphate oxygens. The adsorption which results from the binding between the nucleotide molecule and the salt surface is proposed as being due to electrostatic forces. It was concluded that the adsorption was reversible in nature. The adsorption shows a strong dependence upon ionic strength and decreases with increasing ionic strength. Surface area is shown to be an important factor in evaluating and comparing the magnitude of adsorption of nucleotides onto various mineral salts. The implications of the results of the study are discussed in terms of the importance of soluble mineral salts as adsorption sites in the characterization of the adsorption reactions of an adsorbed template in biogeochemical cycles. 相似文献
30.
Summary Different mushrooms, mosses and corresponding soil samples have been collected mainly from two sites in the alpine region of southwestern Bavaria. At the end of the growthseason, September 1986, gamma spectroscopic analysis showed that the moss-, mould, and needle-layer contained considerably more 134Cs and 137Cs activity per unit fresh weight than eight different species of mushroom. These two isotopes were carried into the biotop mainly as a consequence of the Chernobyl accident. 131J could not be found any more in the samples ca. 5–6 months after the catastrophe. The activity of the cesium isotopes decreased with increasing soil depth. In the mushrooms the activity was relatively high in Xerocomus badius and surprisingly low in Boletus edulis; samples of the latter and of Cantharellus cibarius collected in September 1985 (before the accident) and kept deep frozen contained almost identical amounts of 137Cs as those collected from August to October 1986. Mushrooms contained considerably more of the natural isotope 40K than the needlelayers and the soil samples in the neighbourhood. In all mushrooms except Xerocomus badius the activity of 40K was generally higher than the 137Cs activity. The results indicate that except Xerocomus badius the analyzed mushrooms do not actively take up Cs from the soil, in contrast to K. 相似文献