全文获取类型
收费全文 | 1996篇 |
免费 | 96篇 |
国内免费 | 2篇 |
专业分类
2094篇 |
出版年
2022年 | 10篇 |
2021年 | 23篇 |
2020年 | 13篇 |
2019年 | 13篇 |
2018年 | 20篇 |
2017年 | 12篇 |
2016年 | 49篇 |
2015年 | 61篇 |
2014年 | 79篇 |
2013年 | 139篇 |
2012年 | 100篇 |
2011年 | 94篇 |
2010年 | 64篇 |
2009年 | 63篇 |
2008年 | 106篇 |
2007年 | 101篇 |
2006年 | 108篇 |
2005年 | 90篇 |
2004年 | 95篇 |
2003年 | 94篇 |
2002年 | 107篇 |
2001年 | 39篇 |
2000年 | 46篇 |
1999年 | 40篇 |
1998年 | 29篇 |
1997年 | 20篇 |
1996年 | 20篇 |
1995年 | 27篇 |
1994年 | 20篇 |
1993年 | 20篇 |
1992年 | 30篇 |
1991年 | 28篇 |
1990年 | 28篇 |
1989年 | 29篇 |
1988年 | 17篇 |
1987年 | 19篇 |
1986年 | 13篇 |
1985年 | 18篇 |
1984年 | 11篇 |
1983年 | 16篇 |
1982年 | 13篇 |
1981年 | 25篇 |
1980年 | 21篇 |
1979年 | 13篇 |
1978年 | 15篇 |
1977年 | 12篇 |
1976年 | 13篇 |
1975年 | 16篇 |
1974年 | 14篇 |
1973年 | 10篇 |
排序方式: 共有2094条查询结果,搜索用时 15 毫秒
41.
Leslie E. Bailey Shoji Shibata David G. Seriguchi Peter E. Dresel 《Life sciences》1980,26(13):1061-1068
The effect of dantrolene on the positive inotropic effects (PIE) of three cardiotonic agents was assessed on rat and rabbit atria. Dantrolene (10?5M) had no effect on contractile tension or on the PIE to isoproterenol (10?10?10?7M) or ouabain (10?6?10?4). The dose-response curve for the PIE of anthopleurin-A (AP-A) was shifted to the right in rat and rabbit atria by dantrolene (10?4?10?6M). The maximum effect and the concentration of AP-A required for it remained the same. The results suggest that the PIE of AP-A involves intracellular translocation of calcium, unlike those of isoproterenol and ouabain which require increased transmembrane calcium flux. This conclusion is supported by the observation that the exchange and distribution of the labile calcium involved in excitation-contraction coupling was unaffected by AP-A (10?8M), by dantrolene (10?6M) or by the combination. Therefore, AP-A may produce its cardiotonic effect by a action at an intracellular site, a mechanism unlike that of isoproterenol or ouabain. 相似文献
42.
Four major ALDH isozymes have been identified in human tissues using starch gel electrophoresis and isoelectric focusing. The isozyme bands have been termed as ALDH I, II, III and IV according to their decreasing electrophoretic migration and increasing isoelectric point. The isozymes have been partially purified via preparative isoelectric focusing. Kinetic characteristics of ALDH I and II were found to be quite similar to ALDH enzyme 2 and enzyme 1 described earlier by Greenfield and Pietruszko (Biochem Biophys Acta, 35–45 1977). ALDH III and IV showed a very high Km for propionaldehyde (1.0–1.5 mM at pH 9.5) and were not inhibited by disulfiram at pH 9.5. A variant phenotype of ALDH which lacked in isozyme I was detected in various tissues from Japanese individuals. Comparative kinetic properties of normal and variant enzyme are given. 相似文献
43.
Eiji Ichishima Yoshinori Tsuruda Taro Ushijima Takehiko Nomi Shoji Suzuki Michio Takeuchi Akiko Yamane 《Current microbiology》1980,4(2):85-89
The enzymological, physical, and immunological properties of soluble and bound forms of intracellular acid carboxypeptidase
isolated from fresh mycelia ofAspergillus saitoi are reported. In the broken mycelia, about 60% of the total activity was found in the 2,000×g precipitate, with most of the remainder in the 100,000×g supernantant. The highly purified enzymes, Ia and Ib, from the 100,000×g supernatant were found to be homogeneous by such criteria as disc gel electrophoresis at pH 9.4 The bound enzyme, II, was
solubilized from the 2,000×g precipitate by self-digestion at pH 6.4 and was highly purified by chromotography. The two forms of intracellular enzymes,
the soluble enzymes (Ia and Ib) from the 100,00×g supernatant and the solubilized enzyme (II) from the 2,000×g precipitate, were closely related to, but not completely identical with, the extracellular acid carboxypeptidase. 相似文献
44.
The pharmacological effects of PGE1 (6 and 9 days, 21,250 μg/kg per day subcutaneously) upon the growth and the bone resorption of mammals were studied using the proximal tibia and upper incisor of immature rats along with lead acetate as a time marker, and upon the serum calcium and inorganic phosphorus levels. The following results were obtained. 1. PGE1 hardly affected the body weight or the weight of organs of the rats but apparently inhibited the longitudinal growth of proximal tibia in a dose related manner. 2. PGE1 clearly inhibited not only the longitudinal growth (incisor growth) but also the appositional growth (dentin formation) of incisal dentin. 3. The grade of the inhibitory effect on the growth was in the order of bone growth >dentin formation >incisor growth. 4. The occurrence of osteoporosis due to a low calcium diet was inhibited by the simultaneous administration of PGE1, the mechanism being considered to be mainly due to the inhibitory effect on the bone resorption. 5. PGE1 lowered the level of serum calcium and the lowering effect was not observed in the thyro-parathyroidectomized rat. From the facts that the above effects were exactly the same as those of calcitonin (1), the possibility that the subcutaneous injection of PGE1 may induce a calcitonin-like action, a part of which may dependent on the calcinonin secretion is suggested. 相似文献
45.
M Shoji N L Brackett D M Helfman H P Morris J F Kuo 《Biochemical and biophysical research communications》1978,83(3):1140-1146
The activity level of the newly-identified cyclic CMP phosphodiesterase in the fast-growing Morris hepatoma 3924A was found to be much lower than the control (normal or host) liver. Its level in the slow-growing Morris hepatoma 9618A (a minimal deviation tumor), on the other hand, was the same as the host liver. The level of cyclic AMP phosphodiesterase was higher, whereas that of cyclic GMP phosphodiesterase was lower, in hepatoma 3924A than the control liver. In comparison, the levels of the two enzymes were both depressed in hepatoma 9618A. These findings suggest that depression of cyclic CMP phosphodiesterase may be related to the process and the rate of malignant growth, and that metabolism of cyclic CMP may be more crucial than that of cyclic AMP or cyclic GMP in the neoplastic cell proliferation. 相似文献
46.
Theoretical and experimental studies on viscoelastic properties of erythrocyte membrane. 总被引:22,自引:3,他引:19 下载免费PDF全文
The deformation of a portion of erythrocyte during aspirational entry into a micropipette has been analyzed on the basis of a constant area deformation of an infinite plane membrane into a cylindrical tube. Consideration of the equilibrium of the membrane at the tip of the pipette has generated the relation between the aspirated length and the dimensionless time during deformational entry as well as during relaxation after the removal of aspiration pressure. Experimental studies on deformation and relaxation of normal human erythrocytes were performed with the use of micropipettes and a video dimension analyzer which allowed the continuous recording of the time-courses. The deformation consisted of an initial rapid phase with a membrane viscosity (range 0.6 x 10(-4) to 4 x 10(-4) dyn.s/cm) varying inversely with the degree of deformation and a later slow phase with a high membrane viscosity (mean 2.06 x 10(-2) dyn.s/cm) which was not correlated with the degree of deformation. The membrane viscosity of the recovery phase after 20 s of deformation (mean 5.44 x 10(-4) dyn.s/cm) was also independent of the degree of deformation. When determined after a short period of deformation (e.g., 2 s), however, membrane viscosity of the recovery phase became lower and agreed with that of the deformation phase. These results suggest that the rheological properties of the membrane can undergo dynamic changes depending on the extent and duration of deformation, reflecting molecular rearrangement in response to membrane strain. 相似文献
47.
48.
Embryos excised from winter wheat grains were vernalized for1050 days with or without sugar (sucrose). Determinationswere made of fresh weight, protein-nitrogen, amino-nitrogen,RNA and DNA. There was no change in the contents of RNA of wheatembryos during the vernalization. The incorporation of 32P intonucleic acid in wheat embryos during vernalization in the presenceof sugar was much higher than that of embryos vernalized withoutsugar. From these results we assumed that RNA turnover occurredduring the vernalization. There was no significant differencein the nucleotide composition of RNA extracted between the vernalizedand unvernalized embryos. The RNA of wheat embryos was separatedinto two fractions. Proportions of these two RNA fractions variedin the course of cold treatment, and similar changes were foundin developing wheat leaves. (Received July 25, 1974; ) 相似文献
49.
50.
A new approach to the community-level BIOLOG assay was proposed. This assay, which we call the BIOLOG-MPN assay, is a most-probable-number (MPN) assay that uses BIOLOG plates and multiple sole carbon sources, and the profiles obtained by this assay consist of MPNs estimated for the substrates in the BIOLOG plates. In order to demonstrate the performance of the BIOLOG-MPN assay, it was applied to pure cultures, model bacterial communities that contain two strains in different ratios, and microbial community samples. MPN estimation using BIOLOG plates worked well for the substrates on which utilizers can grow at a sufficiently high rate for color development under the conditions of the assay procedure. Furthermore, the results obtained using model communities showed that the MPNs obtained reflected the mixing ratios of pure cultures in the model communities. The profiles obtained using model communities and community samples were differentiated properly by statistical analyses. The results suggest that the BIOLOG-MPN assay is a promising procedure for obtaining a quantitative picture of the community structure. 相似文献