全文获取类型
收费全文 | 1950篇 |
免费 | 242篇 |
国内免费 | 8篇 |
专业分类
2200篇 |
出版年
2022年 | 22篇 |
2021年 | 28篇 |
2020年 | 11篇 |
2019年 | 17篇 |
2018年 | 26篇 |
2017年 | 18篇 |
2016年 | 43篇 |
2015年 | 89篇 |
2014年 | 84篇 |
2013年 | 94篇 |
2012年 | 131篇 |
2011年 | 115篇 |
2010年 | 84篇 |
2009年 | 67篇 |
2008年 | 100篇 |
2007年 | 101篇 |
2006年 | 100篇 |
2005年 | 80篇 |
2004年 | 86篇 |
2003年 | 61篇 |
2002年 | 61篇 |
2001年 | 64篇 |
2000年 | 58篇 |
1999年 | 76篇 |
1998年 | 28篇 |
1997年 | 28篇 |
1996年 | 21篇 |
1995年 | 21篇 |
1994年 | 16篇 |
1993年 | 19篇 |
1992年 | 50篇 |
1991年 | 39篇 |
1990年 | 39篇 |
1989年 | 30篇 |
1988年 | 36篇 |
1987年 | 29篇 |
1986年 | 26篇 |
1985年 | 21篇 |
1984年 | 16篇 |
1983年 | 14篇 |
1982年 | 11篇 |
1981年 | 10篇 |
1980年 | 12篇 |
1979年 | 12篇 |
1977年 | 12篇 |
1976年 | 9篇 |
1975年 | 10篇 |
1974年 | 10篇 |
1973年 | 11篇 |
1972年 | 10篇 |
排序方式: 共有2200条查询结果,搜索用时 0 毫秒
1.
A patient with chronic anemia is presented who radiologically showed prominent rugae of the stomach. Angiography demonstrated an arteriovenous malformation with a large feeding artery and prominent draining veins. 相似文献
2.
Ultrastructure of the epithelial cells of the ventral prostate from the hopping mouse Notomys alexis
The large ventral prostate of the hopping mouse has abundant secretory units whose epithelial cells vary in height and which often have nuclei in the apical region of the cell. TEM observations indicated two epithelial cell types in which some unusual features occurred. Type A cells had granular endoplasmetic reticulum (GER) whose membranes often formed intracytoplasmic confronting cisternae. Type B cells had more fragmented and vesiculated GER with sparse ribosomes and less frequently also intracytoplasmic confronting confronting cisternae. In the latter cells, two types of granules were found, one of which was derived from the Golgi and the other possibly directly from the GER. Type A cells only had one type of granule present. A highly convoluted membrane was also found at the basal region in many of the cells. The significance of these unusual ultrastructural features has yet to be ascertained. 相似文献
3.
Electron microscope study of the structures of the Bacillus subtilis prophages, SPO2 and phi105 总被引:14,自引:0,他引:14
Circular duplex structures of the correct length are observed in the electron microscope in hybridization mixtures of lysogen DNA and mature phage DNA for the case of the temperate Bacillus subtilis bacteriophage SPO2. This result shows that the sequence order of the prophage is a circular permutation of that of the mature phage. By making heteroduplexes of prophage DNA with that of the SPO2 deletion mutants, R90 and S25, the att site of the phage has been mapped at 61.2 ± 0.6% from one end of the mature phage DNA, which has a length of 38,600 base pairs. In the same co-ordinate system, the R90 deletion extends from 58.9 ± 0.7 to 66.8 ± 0.8% on the SPO2 chromosome, whereas the S25 deletion extends from 63.2 ± 0.6 to 66.9 ± 0.7%. In similar experiments with lysogen and mature phage DNA's of the temperate B. subtilis phage, φ105, no circular structures were seen. This result shows that the sequence order in the prophage and the phage are colinear, without circular permutation. 相似文献
4.
Helen M P Chui May Meroueh Stephen A Scaringe Christine S Chow 《Bioorganic & medicinal chemistry》2002,10(2):325-332
The synthesis of a 5'-O-BzH-2'-O-ACE-protected-3-methyluridine phosphoramidite is reported [BzH, benzhydryloxy-bis(trimethylsilyloxy)silyl; ACE, bis(2-acetoxyethoxy)methyl]. The phosphoramidite was employed in solid-phase RNA synthesis to generate a series of RNA hairpins containing single or multiple modifications, including the common nucleoside pseudouridine. Three 19-nucleotide hairpin RNAs that represent the 1920-loop region (G(1906)-C(1924)) of Escherichia coli 23S ribosomal RNA were generated. Modifications were present at positions 1911, 1915, and 1917. The stabilities and structures of the three RNAs were examined by using thermal melting, circular dichroism, and NMR spectroscopy 相似文献
5.
6.
D A Hartman S R Kuo T R Broker L T Chow R D Wells 《The Journal of biological chemistry》1992,267(8):5488-5494
A conformational distortion in the DNA duplex at the regulatory region of human papillomavirus type-11 next to an intermolecular triplex, formed with a synthetic oligonucleotide, was investigated with several chemical probes. The sequence targeted for triplex formation borders on the binding sites for the regulatory proteins encoded by the viral E2 open reading frame. Dimethyl sulfate, diethyl pyrocarbonate, and OsO4 all react to a greater extent with nucleotides in the duplex that are immediately adjacent to the triplex as compared to other bases throughout the duplex. This hypermodification was observed on both the polypurine and polypyrimidine strands of the duplex DNA. Similar hyperreactivity of bases flanking a triplex also was seen when the contiguous target polypurine tract was effectively extended by mutating interrupting pyrimidines in the human papillomavirus type-11 sequence to purines. We propose that this hyperreactivity is due to a structural distortion caused by the junction between the triplex and the duplex tracts. 相似文献
7.
8.
9.
Z Kleinrok M Sieklucka-Dziuba A Sek E Rodziewicz U Latus 《Acta physiologica Polonica》1987,38(6):477-482
In experiments on male Albino-Swiss mice weighing 18-22 g insulin given in doses of 2 i.u./kg caused no change in the time of reaction to pain, while the same dose administered daily for 7 days potentiated the analgesic action of morphine (3 mg/kg s.c.). Glucose caused no change in this effect of insulin. After 14 days of insulin treatment the time of reaction to pain in the animals subjected to the action of morphine returned to its initial value. Twenty-four hours after the last administration of morphine the level of gamma-aminobutyric acid (GABA) was found to be decreased in the animals receiving insulin with glucose. These results suggest that the central action of insulin is dependent not only on hypoglycaemia produced by it, but may be due also to its direct action on the central structures and an indirect action mediated by its effect on other neurotransmitter systems. 相似文献
10.