全文获取类型
收费全文 | 2640篇 |
免费 | 275篇 |
国内免费 | 1篇 |
出版年
2021年 | 40篇 |
2020年 | 22篇 |
2019年 | 26篇 |
2018年 | 46篇 |
2017年 | 39篇 |
2016年 | 59篇 |
2015年 | 70篇 |
2014年 | 98篇 |
2013年 | 102篇 |
2012年 | 150篇 |
2011年 | 123篇 |
2010年 | 98篇 |
2009年 | 74篇 |
2008年 | 94篇 |
2007年 | 117篇 |
2006年 | 106篇 |
2005年 | 106篇 |
2004年 | 99篇 |
2003年 | 82篇 |
2002年 | 75篇 |
2001年 | 81篇 |
2000年 | 77篇 |
1999年 | 69篇 |
1998年 | 43篇 |
1997年 | 31篇 |
1996年 | 33篇 |
1995年 | 29篇 |
1994年 | 24篇 |
1993年 | 23篇 |
1992年 | 56篇 |
1991年 | 38篇 |
1990年 | 38篇 |
1989年 | 51篇 |
1988年 | 34篇 |
1987年 | 37篇 |
1986年 | 44篇 |
1985年 | 38篇 |
1984年 | 43篇 |
1983年 | 31篇 |
1982年 | 23篇 |
1981年 | 19篇 |
1980年 | 25篇 |
1979年 | 27篇 |
1978年 | 25篇 |
1976年 | 22篇 |
1975年 | 23篇 |
1974年 | 25篇 |
1973年 | 21篇 |
1972年 | 36篇 |
1971年 | 20篇 |
排序方式: 共有2916条查询结果,搜索用时 15 毫秒
81.
Two Types of Genetic Interaction Implicate the Whirligig Gene of Drosophila Melanogaster in Microtubule Organization in the Flagellar Axoneme 总被引:1,自引:1,他引:0
下载免费PDF全文
![点击此处可从《Genetics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The mutant nc4 allele of whirligig (3-54.4) of Drosophila melanogaster fails to complement mutations in an alpha-tubulin locus, alpha 1t, mutations in a beta-tubulin locus, B2t, or a mutation in the haywire locus. However, wrl fails to map to any of the known alpha- or beta-tubulin genes. The extragenic failure to complement could indicate that the wrl product participates in structural interactions with microtubule proteins. The whirligig locus appears to be haploinsufficient for male fertility. Both a deficiency of wrl and possible loss of function alleles obtained by reverting the failure to complement between wrlnc4 and B2tn are dominant male sterile in a genetic background wild type for tubulin. The dominant male sterility of the revertant alleles is suppressed if the flies are also heterozygous for B2tn, for a deficiency of alpha 1t, or for the haync2 allele. These results suggest that it is not the absolute level of wrl gene product but its level relative to tubulin or microtubule function that is important for normal spermatogenesis. The phenotype of homozygous wrl mutants suggests that the whirligig product plays a role in postmeiotic spermatid differentiation, possibly in organizing the microtubules of the sperm flagellar axoneme. Flies homozygous for either wrlnc4 or revertant alleles are viable and female fertile but male sterile. Premeiotic and meiotic stages of spermatogenesis appear normal. However, in post-meiotic stages, flagellar axonemes show loss of the accessory microtubule on the B-subfiber of outer doublet microtubules, outer triplet instead of outer doublet microtubules, and missing central pair microtubules. 相似文献
82.
J A Wass J Williams M Charlesworth D P Kingsley A M Halliday I Doniach L H Rees W I McDonald G M Besser 《BMJ (Clinical research ed.)》1982,284(6333):1908-1911
Bromocriptine has an accepted place in the management of small pituitary tumours that secrete either prolactin or growth hormone. The treatment of large tumours with extrasellar extensions is more difficult, however: though surgery is the standard treatment, it is often unsuccessful in returning excessive hormone secretion to normal and may cause hypopituitarism. A prospective trial was undertaken to assess the frequency with which changes in pituitary function and size of large tumours occurs. Nineteen patients were studied before and during treatment with bromocriptine (7.5 to 60 ml/day) for three to 22 months, using contrast radiology and a detailed assessment of pituitary function. Eighteen patients had hyperprolactinaemia and two of these also had raised concentrations of growth hormones; one patient had an apparently non-functioning tumour. In 12 patients (63%) tumour size decreased with bromocriptine and no tumour enlarged. Nine patients had visual-field defects, which improved in seven, becoming normal in five. Pituitary function improved in nine patients (47%) becoming entirely normal in three. Bromocriptine should be the treatment of choice in patients with large pituitary tumours with extrasellar extensions, provided close supervision is maintained. 相似文献
83.
84.
85.
A permeabilized cell model for studying cell division: a comparison of anaphase chromosome movement and cleavage furrow constriction in lysed PtK1 cells 总被引:12,自引:10,他引:2
下载免费PDF全文
![点击此处可从《The Journal of cell biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
After lysis in a Brij 58-polyethylene glycol medium, PtK1 cells are permeable to small molecules, such as erythrosin B, and to proteins, such as rhodamine-labeled FAB, myosin subfragment-1, and tubulin. Holes are present in the plasma membrane, and the mitochondria are swollen and distorted, but other membrane-bounded organelles of the lysed cell model are not noticeably altered. After lysis, the mitotic apparatus is functional; chromosomes move poleward and the spindle elongates. Cells lysed while in cytokinesis will continue to divide for several minutes. Addition of crude tubulin extracts, MAP-free tubulin, or taxol to the lysis medium retards anaphase chromosome movements but does not affect cleavage. On the other hand, N-ethylmaleimide-modified myosin subfragment-1, phalloidin, and cytochalasin B inhibit cleavage but have no effect on anaphase chromosome movements under identical lysis conditions. These results suggest that actomyosin plays no functional role in anaphase chromosome movement in mammalian tissue culture cells and that microtubule depolymerization is a rate-limiting step for chromosome-to-pole movements. 相似文献
86.
Neurochemical Studies of the Mesolimbic Dopaminergic Pathway: Somatodendritic Mechanisms and GABAergic Neurones in the Rat Ventral Tegmentum 总被引:6,自引:4,他引:2
Abstract: The rat ventral tegmentum (containing dendrites and somata of mesolimbic neurones) contained 1.3 μg/g of dopamine, which was reduced to 40% of the control level by reserpine. Slices of ventral tegmentum were able to accumulate and release (elevated potassium or protoveratrine A) exogenous [3 H]dopamine. In parallel studies the uptake mechanism in ventral tegmentum was shown to be virtually identical to the nerve terminal uptake of [3 H]dopamine by slices of nucleus accumbens. The release of [3 H]dopamine was indistinguishable from that observed in substantia nigra, where there is substantial evidence for dendritic mechanisms. Basal adenylate cyclase activity was present, but dopamine-stimulated activity was not detected. A high GABA concentration (7.7 μmol/g) was present in ventral tegmentum, in conjunction with an uptake and a release mechanism for [3 H]GABA. GABA and muscimol elicited a small, reproducible efflux of [3 H]dopamine, but an interaction between dopamine and [3 H]GABA efflux was not observed. The results are in accord with transmitter roles for dopamine and GABA in the somatoden-dritic area of mesolimbic dopaminergic neurons. 相似文献
87.
Wineries,drosophila, alcohol,and Adh 总被引:1,自引:0,他引:1
R. William Marks John G. Brittnacher John F. McDonald T. Prout F. J. Ayala 《Oecologia》1980,47(1):141-144
Summary Previous workers (McKenzie and Parsons, 1972, 1974; McKenzie, 1974; Briscoe et al., 1975) have found anomalous distributions of species of Drosophila, of sexes of D. melanogaster, and of Adh alleles in and around wineries in Australia and Spain. Field studies in California's Sonoma Valley provide evidence that the explanations advanced for these distributions may incorrect. The anomalous distribution of species was attributed to alcohol, either as a selective agent or as a behavioral stimulus. We find a virtually identical species distribution in the absence of environmental alcohol. The anomalous sex ratio was attributedd to differential survivall of the sexes when raised on alcohol. We present crude evidence thatehe difference may simply be a behavioral response to some product of fermentation, which need not be alcohol. Finally, the allele frequency difference reported from Spain was attributed to differential adult mortality on alcohol. We do not find an allele frequency difference even when alcohol is exposed, and therefore suggest that selection is occurring in pre-adult stages. 相似文献
88.
Bovine gastric mucosal and muscle microsomes synthesize prostaglandins and thromboxane B2 (TXB2) from arachidonic acid (AA). TXB2 and 6-keto-prostaglandin F1α (6-keto-PGF1α) were the major products synthesized by pylorus, body, and cardiac region of the gastric mucosa. Gastric muscle mainly synthesized 6-keto-PGF1α. TXB2 and 6-keto-PGF1α synthesis occurs at an appreciable rate from endogenous precursors but more rapidly with added arachidonate. Prostaglandins E2, F2α and D2 were synthesized in smaller amounts under the conditions studied. 相似文献
89.
90.
Jonathan R. Seals Jay M. McDonald David Bruns Leonard Jarett 《Analytical biochemistry》1978,90(2):785-795
A manual ATPase assay which measures the release of 32Pi from [γ-32P]ATP is described. Sodium dodecyl sulfate is used to terminate the enzyme reaction and extraction of the phophomolybdate complex into xylene: isobutanol is used to separate 32Pi from [γ-32P]ATP for quantitation by scintillation counting. The three-step assay is rapid (75–90 samples/h) and minimizes hydrolysis of ATP due to exposure to acidie conditions. The extraction procedure separates 10−15 to 10−7 mol of 32Pi from aqueous solution with an efficiency of 100,7 ± 0.62%. Less than 1% of unhydrolyzed [γ-32P]ATP is extracted. Extraction efficiency is not affected by protein or salts commonly present in enzyme incubation mixtures. Results obtained with this assay are precise, with an intraassay coefficient of variation of 0.6% and an interassay coefficient of variation of 1.8%. The results are comparable to results obtained with a spectrophotometric assay, with a correlation coefficient of 0,996, though assay performance and sensitivity are greatly improved with the isotopic assay. 相似文献