全文获取类型
收费全文 | 11659篇 |
免费 | 666篇 |
国内免费 | 35篇 |
出版年
2024年 | 18篇 |
2023年 | 113篇 |
2022年 | 355篇 |
2021年 | 598篇 |
2020年 | 358篇 |
2019年 | 451篇 |
2018年 | 498篇 |
2017年 | 371篇 |
2016年 | 520篇 |
2015年 | 615篇 |
2014年 | 723篇 |
2013年 | 900篇 |
2012年 | 971篇 |
2011年 | 867篇 |
2010年 | 512篇 |
2009年 | 410篇 |
2008年 | 525篇 |
2007年 | 498篇 |
2006年 | 446篇 |
2005年 | 437篇 |
2004年 | 341篇 |
2003年 | 287篇 |
2002年 | 249篇 |
2001年 | 122篇 |
2000年 | 114篇 |
1999年 | 92篇 |
1998年 | 67篇 |
1997年 | 38篇 |
1996年 | 42篇 |
1995年 | 46篇 |
1994年 | 32篇 |
1993年 | 36篇 |
1992年 | 56篇 |
1991年 | 49篇 |
1990年 | 57篇 |
1989年 | 45篇 |
1988年 | 46篇 |
1987年 | 35篇 |
1986年 | 35篇 |
1985年 | 40篇 |
1984年 | 35篇 |
1983年 | 31篇 |
1982年 | 26篇 |
1981年 | 30篇 |
1980年 | 18篇 |
1979年 | 17篇 |
1978年 | 22篇 |
1977年 | 20篇 |
1976年 | 23篇 |
1975年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
101.
S C Wong M A Ali J R Pond S M Rubin S E Johnson J B Wilson T H Huisman 《Biochimica et biophysica acta》1984,784(2-3):187-188
A new fast-moving alpha-chain Hb variant with an Asn leads to Asp substitution at position alpha-78 was found in a French-Acadian family living in Eastern Canada. The identical substitution was reported in Hb J-Singapore, which also had an additional Ala leads to Gly substitution at position alpha-79. The new variant, which did not result in any clinical symptoms, was named accordingly, Hb J-Singa. 相似文献
102.
103.
Age-related changes in the composition and structure of human articular-cartilage proteoglycans. 总被引:12,自引:5,他引:7 下载免费PDF全文
1. Analysis of the purified proteoglycans extracted from normal human articular cartilage with 4M-guanidinium chloride showed that there was an age-related increase in their content of protein and keratan sulphate. 2. The hydrodynamic size of the dissociated proteoglycans also decreased with advancing age, but there was little change in the proportion that could aggregate. 3. Results suggested that some extracts of aged-human cartilage had an increased content of hyaluronic acid compared with specimens from younger patients. 4. Dissociated proteoglycans, from cartilage of all age groups, bind to hyaluronic acid and form aggregates in direct proportion to the hyaluronic acid concentration. 5. Electrophoretic heterogeneity of the dissociated proteoglycans was demonstrated on polyacrylamide/agarose gels. The number of proteoglycan species observed was also dependent on the age of the patient. 相似文献
104.
Summary The marrow cavity of the rat tibia was mechanically evacuated and autoimplanted to the subcutaneous tissue. The regenerative process which restored the integrity of marrow stroma and hemopoiesis, was morphometrically evaluated in whole mount of tibia. Following evacuation, the clot filled the cavity. The granulation tissue then appeared and expanded, penetrating and replacing the clot. The fibroblasts of the granulation tissue differentiated into osteoblasts forming osteoid bone. Within its interstices, the primordial marrow consisting of loose connective tissue and vascular sinuses appeared and hemopoiesis resumed. Expansion of hemopoiesis resulted in the resorption of bone and within three weeks the tibial cavity was restored to the pre-evacuation state.Autoradiography indicated that the labeling index was initially high in fibroblasts and osteoblasts but was subsequently reduced while it increased in osteocytes, cells of Haversian canals, stromal and hemopoietic cells of marrow. The finding is in disagreement with the view that the regenerative process originates from the Haversian canal. When the label was introduced on day 4 post-operatively, it subsequently appeared in osteocytes, cells of Haversian canal, stromal elements of the marrow, but not in the hemopoietic cells. This indicates complete dissociation of marrow stroma and hemopoietic stem cell.Supported by NASA Contract NSG 9061. Mehdi Tavassoli is the recipient of a CRD Award AM-70551 相似文献
105.
A.K. Goff J. Zamecnik M. Ali D.T. Armstrong 《Prostaglandins & other lipid mediators》1978,15(5):875-879
The ability of prostaglandin I2 (PGI2) to stimulate cyclic AMP production by granulosa cells, isolated from intact immature rats, has been demonstrated in vitro. The minimal effective dose was 15 ng/ml, which was comparable to the minimal effective dose for PGE2. However, a concentration of 15 μg/ml PGI2 was required to stimulate cyclic AMP production maximally, compared to a concentration of 1 μg/ml PGE2, which produced the maximum response. It therefore appears that PGI2 is not more effective than PGE2 in stimulating cyclic AMP production in granulosa cells, and is possibly less effective. Submaximal concentrations of PGI2 appeared to be able to modify the stimulation of cyclic AMP production by follicle- stimulating hormone (FSH), but whether or not PGI2 plays any role in follicular function remains to be established. 相似文献
106.
Bovine gastric mucosal and muscle microsomes synthesize prostaglandins and thromboxane b/ (TXB2) from aratchidonic acid (AA). TXB2 and 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) were the majro products synthesized by pylorus, body, and cardiac region of the gastric mucosa. Gastric muscle mainly synthesized 6-keto-PGF1 alpha. TXB2 and 6-keto-PGF1 alpha synthesis occurs at an appreciable rate from endogenous precursors but more rapidly with added arachidonate. Prostaglandins E2, F2 alpha and D2 were synthesized in smaller amounts under the conditions studied. 相似文献
107.
Hexokinase is present in the tissues in four isoenzymic forms. Cerebral tissue contains predominantly Type I hexokinase which
is believed to be insulin-insensitive. In cerebral tissue about 60 to 70% of the hexokinase is bound to the particulate fraction.
The changes in the distribution of hexokinase Type I and Type II together with the bound and free hexokinase have been studied
in control, diabetic and diabetic animals treated with insulin. The results indicate that the presence of insulin is essential
for the normal binding of the hexokinase to the particulate fraction. In heart tissue, Type II hexokinase bound to the pellet
shows a significant decrease in diabetes, which is reversed on insulin administration. 相似文献
108.
Summary Microtubules and 10 nm-filaments appear to be involved in the functions of the retinal pigment epithelium (RPE). The presence of microtubules in the RPE of light-adapted eyes, but not in dark-adapted eyes, suggests that they may be involved primarily in organelle movement. On the other hand, the random and constant presence of 10 nm-filaments within the basal portion of the PE implies a cytoskeletal role for these filaments.The authors thank their colleagues Pierre Couillard and Michel Anctil for helpful advice and criticism during the course of this study. Financial support was provided by the C.R.S.N.G. du Canada and the Ministère de l'Education du Québec (F.C.A.C.) 相似文献
109.
The binding of the nonintercalating dye berenil to the 70S ribosome of Escherichia coli has been demonstrated by spectrophotometric measurements and gel filtration through Biogel P100 column. The berenil spectrum is gradually shifted towards the red region with the increasing amount of ribosome added, the isosbestic point being at 375 nm. There is positive cooperativity in the binding of berenil to the ribosome as demonstrated by the equilibrium dialysis. On binding with berenil, the ribosome is degraded faster by RNase I especially at low Mg++ concentration and its capacity to inhibit RNase I catalysed hydrolysis of ribopolymers is decreased. These indicate the unfolding of the structure of the ribosome. 相似文献
110.
Lawrence W. Adler Tomio Ichikawa Syed M. Hasan Tomofusa Tsuchiya Barry P. Rosen 《Journal of cellular biochemistry》1977,7(1):15-27
Membrane vesicles of Escherichia coli can be produced by 2 different methods: lysis of intact cells by passage through a French pressure cell or by osmotic rupturing of spheroplasts. The membrane of vesicles produced by the former method is everted relative to the orientation of the inner membrane in vivo. Using NADH, D-lactate, reduced phenazine methosulfate, or ATP these vesicles produce protonmotive forces, acid and positive inside, as determined using flow dialysis to measured the distribution of the weak base methylamine and the lipophilic anion thiocyanate. The vesicles accumulate calcium using the same energy sources, most likely by a calcium/proton antiport. Calcium accumulation, therefore, is presumably indicative of a proton gradient, acid inside. The latter type of vesicle, on the other hand, exhibits D-lactate-dependent proline transport but does not accumulate calcium with D-lactate as an energy source. NADH oxidation or ATP hydrolysis, however, will drive the transport of calcium but not proline in these vesicles. Oxidation of NADH or hydrolysis of ATP simultaneous with oxidation of D-lactate does not result in either calcium or proline transport. These results suggest that the vesicles are a patchwork or mosiac, in which certain enzyme complexes have an orientation opposite to that found in vivo, resulting in the formation of electrochemical proton gradients with an orientation opposite to that found in the intact cell. Other complexes retain their original orientation, making it possible to set up simultaneous proton fluxes in both directions, causing an apparent uncoupling of energy-linked processes. That the vesicles are capable of generating protonmotive forces of the opposite polarity was demonstrated by measurements of the distribution of acetate and methylamine (to measure the ΔpH) and thiocyanate (to measure the Δψ). 相似文献