全文获取类型
收费全文 | 14941篇 |
免费 | 1393篇 |
国内免费 | 98篇 |
专业分类
16432篇 |
出版年
2023年 | 65篇 |
2022年 | 197篇 |
2021年 | 303篇 |
2020年 | 172篇 |
2019年 | 220篇 |
2018年 | 257篇 |
2017年 | 235篇 |
2016年 | 410篇 |
2015年 | 723篇 |
2014年 | 739篇 |
2013年 | 922篇 |
2012年 | 1109篇 |
2011年 | 1092篇 |
2010年 | 660篇 |
2009年 | 605篇 |
2008年 | 843篇 |
2007年 | 788篇 |
2006年 | 736篇 |
2005年 | 702篇 |
2004年 | 633篇 |
2003年 | 618篇 |
2002年 | 560篇 |
2001年 | 280篇 |
2000年 | 259篇 |
1999年 | 232篇 |
1998年 | 156篇 |
1997年 | 107篇 |
1996年 | 122篇 |
1995年 | 96篇 |
1994年 | 90篇 |
1993年 | 106篇 |
1992年 | 161篇 |
1991年 | 129篇 |
1990年 | 127篇 |
1989年 | 137篇 |
1988年 | 99篇 |
1987年 | 112篇 |
1986年 | 104篇 |
1985年 | 106篇 |
1984年 | 81篇 |
1983年 | 89篇 |
1982年 | 85篇 |
1981年 | 74篇 |
1980年 | 70篇 |
1979年 | 102篇 |
1978年 | 91篇 |
1977年 | 64篇 |
1976年 | 67篇 |
1974年 | 66篇 |
1973年 | 62篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
Extracellular suppression allows mating by pheromone-deficient sterile mutants of Saccharomyces cerevisiae 总被引:14,自引:1,他引:13 下载免费PDF全文
MAT alpha haploids with mutations in the STE13 or KEX2 gene, and MATa haploids with mutations in the STE6 or STE14 gene, do not mate with wild-type cells of the opposite mating type. We found that such mutants were able to mate with partners that carry mutations (sst1 and sst2) that cause cells to be supersensitive to yeast mating pheromone action. Mating ability of MAT alpha ste13 and MAT alpha kex2 mutants could also be restored by adding normal MAT alpha cells to mating mixtures or by adding just the appropriate purified pheromone (alpha-factor). Therefore, the mating deficiencies caused by the ste13 and kex2 lesions, and by inference, the ste6 and ste14 mutations, appear to result only from secretion of an insufficient amount of pheromone or a nonfunctional pheromone. 相似文献
12.
Michitaro Nagasawa James Amigo Chan Charles J. Sih 《Prostaglandins & other lipid mediators》1974,8(3):221-230
Prostaglandins E1, F1α and A2 were covalently joined to the surface of Sepharose as carboxamide linkages. The insolubilized prostaglandins were shown to function effectively in the purification of 15(S) -hydroxyprostaglandin dehydrogenase. 相似文献
13.
14.
The three potent antimitotic vinca alkaloids: vincristine (VCR), vinblastine (VLB), and vindesine (VDS) were compared for their effect in blocking axoplasmic transport in vitro using a desheathed preparation of the peroneal branch of cat sciatic nerve. A range of vinca alkaloid concentrations from 1–100μM was examined. The relative order of potency in blocking axoplasmic transport was VCR > VLB > VDS at a concentration of 25μM. At the higher concentrations block occurred so rapidly that a statistically significant difference between these agents could not be obtained. The relation of vinca block ot the transport mechanism is discussed. 相似文献
15.
16.
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
17.
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
18.
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
19.
Abstract. Contrary to current assumptions, the reflex blood of two-spot ladybirds, Adalia bipunctata , and seven-spot ladybirds, Coccinella septempunctata , contains haemocyte-like cells. Furthermore, DNA can be extracted and amplified from coccinellid reflex blood, confirming the presence of haemocyte-like cells and demonstrating a nondestructive method of DNA extraction. 相似文献
20.
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