全文获取类型
收费全文 | 2467篇 |
免费 | 207篇 |
国内免费 | 4篇 |
出版年
2022年 | 9篇 |
2021年 | 44篇 |
2020年 | 18篇 |
2019年 | 19篇 |
2018年 | 24篇 |
2017年 | 20篇 |
2016年 | 56篇 |
2015年 | 106篇 |
2014年 | 124篇 |
2013年 | 121篇 |
2012年 | 183篇 |
2011年 | 181篇 |
2010年 | 108篇 |
2009年 | 87篇 |
2008年 | 122篇 |
2007年 | 106篇 |
2006年 | 124篇 |
2005年 | 97篇 |
2004年 | 115篇 |
2003年 | 102篇 |
2002年 | 87篇 |
2001年 | 79篇 |
2000年 | 84篇 |
1999年 | 60篇 |
1998年 | 31篇 |
1997年 | 25篇 |
1996年 | 21篇 |
1995年 | 14篇 |
1994年 | 22篇 |
1993年 | 8篇 |
1992年 | 31篇 |
1991年 | 44篇 |
1990年 | 23篇 |
1989年 | 36篇 |
1988年 | 27篇 |
1987年 | 47篇 |
1986年 | 27篇 |
1985年 | 36篇 |
1984年 | 28篇 |
1983年 | 20篇 |
1982年 | 16篇 |
1981年 | 12篇 |
1980年 | 7篇 |
1979年 | 22篇 |
1978年 | 15篇 |
1977年 | 17篇 |
1976年 | 8篇 |
1975年 | 12篇 |
1974年 | 16篇 |
1973年 | 9篇 |
排序方式: 共有2678条查询结果,搜索用时 250 毫秒
1.
2.
3.
4.
5.
A simple and rapid method for preparing [32P]adenosine 3'5'-cyclic monophosphate (cAMP) is described. A culture of an Escherichia coli mutant which excretes cAMP about 150 times faster than does a wild-type strain was incubated overnight with [32P]orthophosphate of high specific activity (e.g., 4000 Ci/mol (1 Ci = 37 GBq). The [32P]cAMP which accumulated extracellularly was then purified to 99.9% radiochemical purity in less than 4 h by adsorption to charcoal and alumina column chromatography. A two-dimensional chromatography system using a PEI-cellulose plate is also described which should prove useful for studying cAMP metabolism with 32P- or 3H-labeled cAMP or ATP. 相似文献
6.
Four myeloid cell lines (M1, WEHI-3B D+, FDC-P1, and 32D) were screened for the presence of J11d antigen. One of these cell lines, the myeloid leukemia M1, was found to express a high level of J11d antigen on the cell surface. Recombinant mouse leukemic inhibitory factor (rm-LIF), recombinant human LIF (rh-LIF), and steroids (hydrocortisone and dexamethasone) could induce M1 cells to undergo monocytic differentiation. The level of J11d antigen was greatly reduced after treatment of the cells with LIF or steroids. Western blotting revealed that the apparent molecular weight of the J11d antigen on M1 cells was 45-48 kDa. Furthermore, the level of J11d mRNA was also reduced during LIF-induced differentiation of M1 cells. 相似文献
7.
K. Y. E. Leung M. van Stralen M. G. Danilouchkine G. van Burken M. L. Geleijnse J. H. C. Reiber N. de Jong A. F. W. van der Steen J. G. Bosch 《Netherlands heart journal》2011,19(6):307-310
Real-time three-dimensional (3D) ultrasound imaging has been proposed as an alternative for two-dimensional stress echocardiography for assessing myocardial dysfunction and underlying coronary artery disease. Analysis of 3D stress echocardiography is no simple task and requires considerable expertise. In this paper, we propose methods for automated analysis, which may provide a more objective and accurate diagnosis. Expert knowledge is incorporated via statistical modelling of patient data. Methods for identifying anatomical views, detecting endocardial borders, and classification of wall motion are described and shown to provide favourable results. We also present software developed especially for analysis of 3D stress echocardiography in clinical practice. Interobserver agreement in wall motion scoring is better using the dedicated software (96%) than commercially available software not dedicated for this purpose (79%). The developed tools may provide useful quantitative and objective parameters to assist the clinical expert in the diagnosis of left ventricular function. 相似文献
8.
Amy Chapman Gonzalo Gonzales Wayne R. Burrowes Paul Assanah Bernadette Iannone Michael K. Leung George B. Stefano 《Cellular and molecular neurobiology》1984,4(2):143-155
In Mytilus and Leucophaea the high-affinity binding site density is significantly lower in old animals than in young animals, whereas the low-affinity site density remains unchanged. In Mytilus the estimated met-enkephalin and met-enkephalin-Arg6-Phe7 levels are significantly higher in old than in young animals. In Leucophaea only the met-enkephalin level can be determined, and it is also higher in old animals. The decrease in the high-affinity binding site density and the corresponding increase in endogenous enkephalin levels suggest the existence of an opioid compensatory mechanism associated with the aging process. In Mytilus there is a demonstrated decrease with age in intraganglionic dopamine levels in response to applied opiates. In addition, the inhibition of dopamine-stimulated adenylate cyclase activity by opiates also decreases in older animals. In Leucophaea the sex difference in opioid binding densities diminishes with age. 相似文献
9.
DNA from bovine x hamster hybrid cells preferentially segregating bovine chromosomes has been analyzed by blot hybridization with alpha and beta interferon probes. Retention or loss of bovine interferon genes was compared to segregation of bovine isozyme loci representing previously described syntenic groups. Families of bovine alpha (IFNA) and beta (IFNB) interferon genes were segregated in concordance with each other and with aconitase-1 (ACO1) on bovine syntenic group U18. This syntenic relationship is conserved on human chromosome 9p and on the portion of mouse chromosome 4 proximal to the centromere. In addition, cattle restriction fragment length polymorphisms were identified with both IFNA and IFNB probes. Of particular interest is a polymorphism apparently due to duplication of IFNB genes. 相似文献
10.
Q Yuan W M Jiang D Hollander E Leung J D Watson G W Krissansen 《Biochemical and biophysical research communications》1991,176(3):1443-1449
A cDNA clone encoding the N-terminal sequence of the murine integrin beta 7 subunit, a novel member of the leukocyte cell adhesion molecule subset (Leu-CAM), has been isolated. An N-terminal region of 13 contiguous amino acids deduced from the cDNA shows complete identity with the N-terminus of the 120 kDa subunit of the M290 antigen, a surface molecule found highly expressed on mouse intestinal intraepithelial lymphocytes (IEL). This unexpected result focuses two previously unconnected areas of research and suggests that integrins may have a special role to play in the defence of the gut mucosa. 相似文献