全文获取类型
收费全文 | 61819篇 |
免费 | 4160篇 |
国内免费 | 18篇 |
专业分类
65997篇 |
出版年
2023年 | 423篇 |
2022年 | 892篇 |
2021年 | 1639篇 |
2020年 | 1041篇 |
2019年 | 1325篇 |
2018年 | 1741篇 |
2017年 | 1494篇 |
2016年 | 2311篇 |
2015年 | 3377篇 |
2014年 | 3613篇 |
2013年 | 4710篇 |
2012年 | 5413篇 |
2011年 | 5063篇 |
2010年 | 3126篇 |
2009年 | 2702篇 |
2008年 | 3647篇 |
2007年 | 3499篇 |
2006年 | 3165篇 |
2005年 | 2775篇 |
2004年 | 2607篇 |
2003年 | 2443篇 |
2002年 | 2177篇 |
2001年 | 628篇 |
2000年 | 478篇 |
1999年 | 552篇 |
1998年 | 508篇 |
1997年 | 383篇 |
1996年 | 358篇 |
1995年 | 304篇 |
1994年 | 318篇 |
1993年 | 284篇 |
1992年 | 255篇 |
1991年 | 229篇 |
1990年 | 215篇 |
1989年 | 190篇 |
1988年 | 162篇 |
1987年 | 169篇 |
1986年 | 129篇 |
1985年 | 153篇 |
1984年 | 155篇 |
1983年 | 108篇 |
1982年 | 112篇 |
1981年 | 111篇 |
1980年 | 99篇 |
1979年 | 108篇 |
1978年 | 61篇 |
1977年 | 72篇 |
1976年 | 57篇 |
1975年 | 75篇 |
1973年 | 73篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
40 pelvic preparations of rabbits (oryctolagus cuniculus) were bilaterally studied by dissection under the stereomicroscope and angiography. The arterial pattern of the pelvis, i.e. origin and branching of the umbilical, urogenital and internal pudendal arteries (visceral branches), is described. The main characteristics observed are as follows: (1) The umbilical artery is permeable in adults and gives origin to the cranial vesical artery and a caudal branch that irrigates the pelvic urogenital organs and, eventually, the rectum, with six patterns of branching in both sexes. (2) Usually, the urogenital artery is the continuation of the visceral branch of the internal iliac artery. In 1 animal, unilaterally, it arises from the median sacral artery. In 12 animals (6 bilaterally and 6 unilaterally) the urogenital artery is absent. When present, it forms two branches, a cranial and a caudal one, that irrigate of the urogenital organs in both sexes. (3) The internal pudendal artery is the direct continuation of the internal iliac artery and gives to rise to some visceral branches that irrigate the penis, bulbourethral gland and rectum (with six patterns of branching) in males, and the vagina, clitoris and rectum (with three patterns of branching) in females. 相似文献
72.
Organic matter sedimented within salt deposits from the Carboniferous Perm epoch has been investigated for hydrocarbons by gas-liquid-chromatography, mass spectrometry, and spectropolarimetry. Main constituents were made of aliphatic and olefinic hydrocarbons which retained a considerable part of their optical activity thus resisting complete racemization over 250 mio years. 相似文献
73.
Odile Gateau Maria Rocha de Morillo Pierre Louisot Renée Morelis 《生物化学与生物物理学报:生物膜》1980,595(1):157-160
A sialyl transferase activity is found in purified mitochondria. It is not due to residual contamination and this enzymatic system is located in the outer mitochondrial membrane. This proves mitochondrial autonomy in regard to glycoconjugate sialylation. 相似文献
74.
Achiléa Lisboa Bittencourt Maria das Graças Santana Araujo Maria do Socorro Fontoura Paes 《Mycopathologia》1980,71(3):155-158
A case of a two-year-old boy with multiple subcutaneous lesions caused by Basidiobolus haptosporus is presented.The child had also a non-toxic familial goiter and clinical and radiological features of a pulmonary illness. The pulmonary manifestations only disappeared with the treatment with potassium iodide. The authors think that the pulmonary lesions must have arisen by direct spread of the fungus from the subcutaneous lesions of the chest. 相似文献
75.
Summary A 2-year-old girl had a de novo duplication in the long arm of one chromosome 7 and an increased level of the enzyme -glucuronidase in cultured fibroblasts. The phenotype of the girl partly overlaps those of two presumptive syndromes due to secondary partial trisomies 7q. The ratio of the enzyme activity was 1.43 to the controls, and 1.37 to her parent's values. We could not define the abnormality but suggest two alternatives: either the patient is trisomic for region q112 to q22 or for the region q22 to q34. If the second alternative is correct the locus for -glucuronidase is possibly assigned to band 7q22. 相似文献
76.
Summary A large pedigree with a satellited Yq chromosome is described, Q, C, and NOR banding were performed. Family C proband suffers from a Klinefelter syndrome. 相似文献
77.
78.
Chlorine concentrations below 0.8 mg/liter inactivated poliovirus without causing separation of the viral components. These results indicate that the release of RNA from the capsids is the result, not the cause, of virus inactivation by chlorine. 相似文献
79.
Summary The optimum conditions forAcetobacter immobilization were investigated. The results show that: 1) the maximum oxygen uptake rate (OURm) and cell release are related to alginate and cell concentration in the gel; 2)different alginate concentration does not affect cell viability, but long storage in CaCl2 reduces the number of living cells; 3)the double alginate gel layers had no influence on cell viability and on the OURm and prevented cell leakage from the gel matrix. 相似文献
80.
Trehalase activity decreased in 95% at the onset of the transition phase of growth of S. cerevisiae. The question which we raised was whether this phenomenon was due to proteolysis or to conversion of the enzyme to a less active form (dephosphorylation). Immunological methods allowed to identify the presence of the trehalase protein during cell growth. At the same stage of growth, an increase in the non-phosphorylated enzyme was detected "in vitro". Results utilizing mutant strains also indicated that regulation occurred by interconversion of forms. The same mechanism also seems to control trehalase activity in non proliferating conditions. 相似文献