全文获取类型
收费全文 | 6826篇 |
免费 | 639篇 |
国内免费 | 148篇 |
出版年
2022年 | 66篇 |
2021年 | 90篇 |
2020年 | 84篇 |
2019年 | 93篇 |
2018年 | 86篇 |
2017年 | 92篇 |
2016年 | 145篇 |
2015年 | 291篇 |
2014年 | 264篇 |
2013年 | 315篇 |
2012年 | 406篇 |
2011年 | 371篇 |
2010年 | 283篇 |
2009年 | 194篇 |
2008年 | 294篇 |
2007年 | 272篇 |
2006年 | 258篇 |
2005年 | 279篇 |
2004年 | 236篇 |
2003年 | 196篇 |
2002年 | 182篇 |
2001年 | 188篇 |
2000年 | 174篇 |
1999年 | 212篇 |
1998年 | 101篇 |
1997年 | 75篇 |
1996年 | 107篇 |
1995年 | 76篇 |
1994年 | 74篇 |
1993年 | 80篇 |
1992年 | 189篇 |
1991年 | 137篇 |
1990年 | 139篇 |
1989年 | 170篇 |
1988年 | 135篇 |
1987年 | 129篇 |
1986年 | 102篇 |
1985年 | 127篇 |
1984年 | 102篇 |
1983年 | 77篇 |
1982年 | 57篇 |
1981年 | 53篇 |
1980年 | 51篇 |
1979年 | 73篇 |
1978年 | 56篇 |
1977年 | 41篇 |
1974年 | 56篇 |
1973年 | 37篇 |
1972年 | 36篇 |
1971年 | 38篇 |
排序方式: 共有7613条查询结果,搜索用时 15 毫秒
51.
Stimulation by glycerate 2,3-bisphosphate: a common property of cytosolic IMP-GMP 5'-nucleotidase in rat and human tissues 总被引:1,自引:0,他引:1
F Bontemps M F Vincent F Van den Bergh G van Waeg G Van den Berghe 《Biochimica et biophysica acta》1989,997(1-2):131-134
Glycerate 2,3-bisphosphate, a potent stimulator of the cytosolic 5'-nucleotidase which preferentially hydrolyzes IMP and GMP in human erythrocytes (Bontemps et al., 1988, Biochem. J. 250, 687-696), also stimulates the dephosphorylation of IMP in cytosol fractions of rat heart, liver, brain, kidney, spleen and erythrocytes, and of human polymorphonuclear leucocytes, mixed peripheral blood lymphocytes, platelets and fibroblasts. Depending on the cell type, stimulation by 5 mM glycerate 2,3-bisphosphate varied from 1.5- to 12-fold. Where investigated, glycerate 2,3-bisphosphate had an approx. 5-fold higher affinity for the enzyme than its other stimulator, ATP. These observations provide a useful tool to distinguish IMP-GMP 5'-nucleotidase from other 5'-nucleotidases, and suggest a common origin of the cytosolic IMP-GMP 5'-nucleotidase in various tissues. 相似文献
52.
Normal phenotype and slight mental retardation in de novo distal 8p deletion (8pter----8p23.1:) 总被引:1,自引:0,他引:1
In this report we present a 9-year-old boy with mental retardation, behavioural problems and terminal deletion of the short arm of chromosome 8(8pter----8p23.1:). In contrast with previously reported patients with larger terminal and interstitial 8p deletions he did not present major phenotypic abnormalities. 相似文献
53.
P. H. J. F. van den Boogert H. Reinartz K. A. Sjollema M. Veenhuis 《Antonie van Leeuwenhoek》1989,56(2):161-174
The mycoparasitic interactions of Verticillium biguttatum with Rhizoctonia solani and with a variety of other soil-borne fungi were investigated in dual cultures. V. biguttatum interacted with various soil fungi by appressed growth along the host hyphae and infrequent penetrations. Intracellular growth and subsequent sporulation, however, only occurred with R. solani, a few binucleate Rhizoctonia and Ceratobasidium spp., and Sclerotinia sclerotiorum. Effective mycoparasitism on sclerotia was restricted to those belonging to R. solani.Electron-microscopic observations revealed that V. biguttatum can penetrate the host cell with infection tubes. This process is probably mediated by enzymatic hydrolysis of the cell wall. Subsequently, trophic hyphae develop within the host cytoplasm, ultimately resulting in death of the host cell. 相似文献
54.
Partial duplication of the short arm of chromosome 2 (dup(2)(p13----p21) associated with mental retardation and an Aarskog-like phenotype 总被引:2,自引:0,他引:2
In this report we describe a 3-year-old boy with partial trisomy of the short arm of chromosome 2 due to a de novo tandem duplication 2(dup(2)(p13----p21)). In addition to severe growth retardation and moderate psychomotor delay he presented a dysmorphic syndrome compatible with the clinical diagnostic of Aarskog syndrome. 相似文献
55.
Choroideremia and deafness with stapes fixation: a contiguous gene deletion syndrome in Xq21. 总被引:13,自引:6,他引:7 下载免费PDF全文
D E Merry J G Lesko D M Sosnoski R A Lewis M Lubinsky B Trask G van den Engh F S Collins R L Nussbaum 《American journal of human genetics》1989,45(4):530-540
The study of contiguous gene deletion syndromes by using reverse genetic techniques provides a powerful tool for precisely defining the map location of the genes involved. We have made use of individuals with overlapping deletions producing choroideremia as part of a complex phenotype, to define the boundaries on the X chromosome for this gene, as well as for X-linked mixed deafness with perilymphatic gusher (DFN3). Two patients with deletions and choroideremia are affected by an X-linked mixed conductive/sensorineural deafness; one patient, XL-62, was confirmed at surgery to have DFN3, while the other patient, XL-45, is suspected clinically to have the same disorder. A third choroideremia deletion patient, MBU, has normal hearing. Patient XL-62 has a cytogenetically detectable deletion that was measured to be 7.7% of the X chromosome by dual laser flow cytometry; the other patient, XL-45, has a cytogenetically undetectable deletion that measures only 3.3% of the X chromosome. We have produced a physical map of the X-chromosome region containing choroideremia and DFN3 by using routine Southern blotting, chromosome walking and jumping techniques, and long-range restriction mapping to generate and link anonymous DNA sequences in this region. DXS232 and DXS233 are located within 450 kb of each other on the same SfiI and MluI fragments and share partial SalI fragments of 750 and greater than 1,000 kb but are separated by at least one SalI site. In addition, DXS232, which lies outside the MBU deletion, detects the proximal breakpoint of this deletion. We have isolated two new anonymous DNA sequences by chromosome jumping from DXS233; one of these detects a new SfiI fragment distal to DXS233 in the direction of the choroideremia gene, while the other jump clone is proximal to DXS233 and detects a new polymorphism. These data refine the map around the loci for choroideremia and for mixed deafness with stapes fixation and will provide points from which to isolate candidate gene sequences for these disorders. 相似文献
56.
An Xp22 microdeletion associated with ocular albinism and ichthyosis: approximation of breakpoints and estimation of deletion size by using cloned DNA probes and flow cytometry. 总被引:5,自引:3,他引:2 下载免费PDF全文
R E Schnur B J Trask G van den Engh H H Punnett M Kistenmacher M A Tomeo R E Naids R L Nussbaum 《American journal of human genetics》1989,45(5):706-720
Ocular albinism of the Nettleship-Falls type (OA1) and X-linked ichthyosis (XI) due to steroid sulfatase (STS) deficiency are cosegregating in three cytogenetically normal half-brothers. The mother has patchy fundal hypopigmentation consistent with random X inactivation in an OA1 carrier. Additional phenotypic abnormalities that have been observed in other STS "deletion syndromes" are not present in this family. STS is entirely deleted on Southern blot in the affected males, but the loci MIC2X, DXS31, DXS143, DXS85, DXS43, DXS9, and DXS41 are not deleted. At least part of DXS278 is retained. Flow cytometric analysis of cultured lymphoblasts from one of the XI/OA1 males and his mother detected a deletion of about 3.5 million bp or about 2% of the X chromosome. Southern blot and RFLP analysis in the XI/OA1 family support the order tel-[STS-OA1-DXS278]-DXS9-DXS41-cen. An unrelated patient with the karyotype 46,X,t(X;Y) (p22;q11) retains the DXS143 locus on the derivative X chromosome but loses DXS278, suggesting that DXS278 is the more distal locus and is close to an XI/OA1 deletion boundary. If a contiguous gene deletion is responsible for the observed XI/OA1 phenotype, it localizes OA1 to the Xp22.3 region. 相似文献
57.
Y M Marijnen D de Korte W A Haverkort E J den Breejen A H van Gennip D Roos 《Biochimica et biophysica acta》1989,1012(2):148-155
The incorporation of radioactive precursors into purine and pyrimidine nucleotides via 'de novo' and 'salvage' pathways was measured in normal lymphocytes, resting as well as proliferating, and lymphoblastic cell-line cells (MOLT-3). Lymphocytes stimulated with anti-CD3 were taken as actively proliferating lymphocytes (35% in the S-phase, 40 h after stimulation). The incorporation of the precursors in the purine and pyrimidine ribonucleotides was measured by a combination of anion-exchange high-performance liquid chromatography (HPLC) and on-line radioactivity measurement. The actively proliferating normal lymphocytes and MOLT-3 cells incorporated 30-500 times more of the various precursors in the ribonucleotides compared to normal resting lymphocytes. The imbalance in the nucleotide pool found in proliferating normal and lymphoblastic cells was reflected in the incorporation pattern of the various precursors. The activities of the branch-point enzymes IMP dehydrogenase and CTP synthetase most likely determine the differences in the composition of the nucleotide pools between resting and proliferating cells. 相似文献
58.
E Middelkoop A Coppens M Llanillo E E Van der Hoek A J Slotboom B H Lubin J A Op den Kamp L L Van Deenen B Roelofsen 《Biochimica et biophysica acta》1989,978(2):241-248
The ATP-dependent translocation of phospholipids in the plasma membrane of intact Friend erythroleukemic cells (FELCs) was studied in comparison with that in the membrane of mature murine erythrocytes. This was done by following the fate of radiolabeled phospholipid molecules, previously inserted into the outer monolayer of the plasma membranes by using a non-specific lipid transfer protein. The transbilayer equilibration of these probe molecules was monitored by treating the cells--under essentially non-lytic conditions--with phospholipases A2 of different origin. Rapid reorientations of the newly introduced aminophospholipids in favour of the inner membrane leaflet were observed in fresh mouse erythrocytes; the inward translocation of phosphatidylcholine (PC) in this membrane proceeded relatively slow. In FELCs, on the other hand, all three glycerophospholipids equilibrated over both halves of the plasma membrane very rapidly, i.e. within 1 h; nevertheless, an asymmetric distribution in favour of the inner monolayer was only observed for phosphatidylserine (PS). Lowering the ATP-level in the FELCs caused a reduction in the rate of inward translocation of both aminophospholipids, but not of that of PC, indicating that this translocation of PS and phosphatidylethanolamine (PE) is clearly ATP-dependent. Hence, the situation in the plasma membrane of the FELC is rather unique in a sense that, though an ATP-dependent translocase is present and active both for PS and PE, its activity results in an asymmetric distribution of PS, but not of PE. This remarkable situation might be the consequence of the fact that, in contrast to the mature red cell, this precursor cell still lacks a complete membrane skeletal network. 相似文献
59.
In this report we present follow-up on two moderately mentally retarded boys with Aarskog syndrome. As 22 other mentally normal Aarskog patients these two boys presented a catch-up after a delayed puberty with a final adult height of 160 cm. A remarkable finding was the development of macroorchidism in two mentally retarded Aarskog patients. The pathogenesis of macroorchidism in the fragile X syndrome and in other X-linked mental retardation syndromes is discussed. 相似文献
60.
Role of protein synthesis in the accumulation of ferritin mRNA during exposure of cells to iron. 总被引:1,自引:0,他引:1 下载免费PDF全文
The iron-induced biosynthesis of ferritin is regulated at the translational level via multiple mechanism. A prolonged exposure of cells to iron leads to a marked increase in ferritin mRNA levels caused by stabilization of the message. Here we show that this stabilization requires the synthesis de novo of an iron-inducible protein factor. 相似文献