全文获取类型
收费全文 | 5724篇 |
免费 | 440篇 |
国内免费 | 10篇 |
出版年
2023年 | 16篇 |
2022年 | 11篇 |
2021年 | 78篇 |
2020年 | 85篇 |
2019年 | 115篇 |
2018年 | 146篇 |
2017年 | 111篇 |
2016年 | 152篇 |
2015年 | 268篇 |
2014年 | 308篇 |
2013年 | 379篇 |
2012年 | 504篇 |
2011年 | 443篇 |
2010年 | 260篇 |
2009年 | 246篇 |
2008年 | 367篇 |
2007年 | 307篇 |
2006年 | 288篇 |
2005年 | 284篇 |
2004年 | 230篇 |
2003年 | 237篇 |
2002年 | 182篇 |
2001年 | 158篇 |
2000年 | 133篇 |
1999年 | 128篇 |
1998年 | 49篇 |
1997年 | 57篇 |
1996年 | 43篇 |
1995年 | 38篇 |
1994年 | 31篇 |
1993年 | 33篇 |
1992年 | 55篇 |
1991年 | 46篇 |
1990年 | 38篇 |
1989年 | 47篇 |
1988年 | 38篇 |
1987年 | 32篇 |
1986年 | 27篇 |
1985年 | 24篇 |
1984年 | 17篇 |
1983年 | 21篇 |
1982年 | 11篇 |
1980年 | 9篇 |
1979年 | 13篇 |
1978年 | 15篇 |
1976年 | 13篇 |
1975年 | 8篇 |
1974年 | 9篇 |
1972年 | 8篇 |
1971年 | 8篇 |
排序方式: 共有6174条查询结果,搜索用时 31 毫秒
91.
E. M. Lynch J. Wharton M. G. Bryant S. R. Bloom J. M. Polak MD MRCPath M. G. Elder 《Histochemistry and cell biology》1980,67(2):169-177
Summary VIP-like immunoreactive material is present in the female reproductive tract, with a distinct pattern of distribution. The highest concentrations of extractable material and immunoreactive nerve fibres were found in the cervix and vagina. In the cervix these fibres were seen below the surface epithelium and around cervical glands as well as in association with blood vessels and smooth muscle bundles. In the vagina the nerve fibres were most abundant in the superficial regions of the lamina propria. Scattered fibres were also present in the rest of the uterus and in the fallopian tubes. Chromatographic evidence indicates that this VIP-like material is of a similar molecular size to that extracted from other organs. Possible roles for VIP in the regulation of myometrial activity and of cervical and vaginal dilation and secretion are proposed. 相似文献
92.
Proton transport by bacteriorhodopsin in planar membranes assembled from air-water interface films 下载免费PDF全文
Bacteriorhodopsin, in known amounts and controlled orientation, is incorporated into planar membrane films. These films are formed by the sequential transfer of two air-water interface films onto a thin, hydrophilic, electrically conductive support cast from nitrocellulose. The films are easily accessible to electrical measurements and to control of the ionic milieu on either side of the membrane. The area of the assembled membrane films can be varied between 2.3 x 10(-2) cm2 and 0.7 cm2. Illumination of these films produces photocurrents, photovoltages, and changes in the pH of the surrounding medium. The peak amplitude of the photocurrent increases linearly with light intensity for dim lights, and it approaches a saturating value for brighter lights. In the linear range, the stoichiometry of transport is 0.65 +/- 0.06 protons/absorbed photon. The rate of transport is linearly proportional to light at all intensities tested. The amplitude and kinetics of the photovoltage measured are accurately predicted by the photocurrent generated and the passive electrical features of the film. Parallel measurements of pH and photocurrent reveal that the light-induced changes in pH are fully accounted for by the rate and amount of charge transport across the membrane. Preceding the transport of protons, a transient photovoltage is detected that exhibits no detectable latency, reaches peak in about 80 microseconds, and probably arises from light-induced intramolecular charge displacements. 相似文献
93.
Bean plants grown in a controlled temperature glasshouse athigh temperatures (33/28, 30/25, or 27/22 °C) during theperiod of seed development and maturation matured early andproduced small seeds. The seeds were of lower vigour than thosegrown at 21/16 or 18/13 °C. The detrimental effect of highmaturation temperatures was observed even on plants bearingwell-developed seeds (yellow, fleshy-pod stage). Seeds maturedat high temperatures were also more susceptible to deteriorationwith delay in harvest, and to mechanical damage. Heavy wateringof plants with seed ready to harvest caused a reduction in seedvigour. For optimum quality bean seed, it appears essentialthat the seed develops and matures at cool temperatures, ina dry environment. 相似文献
94.
Jean Jew M.D. Bang-H. Hwang Dean Sandquist Terence H. Williams 《Cell and tissue research》1979,202(2):241-249
Summary The question of age as a possible factor influencing the regenerative response of catecholaminergic varicosities in the hypothalamus was investigated in the supraoptic commissure and the paraventricular, periventricular, and dorsomedial hypothalamic nuclei of rats that had received intraventricular injections of the neurotoxin 6-hydroxydopamine when they were (1) neonates, (2) young adults, or (3) senescent adults. After postneurotoxin survival for 4, 21, 56, or 180 days, the animals were perfused, and the hypothalamic tissue sections were cut and processed using a glyoxylic acid method for localizing catecholamines. Four days following neurotoxin administration, counts of fluorescent varicosities showed a significant loss of catecholamine varicosities in each of the four areas. Subsequently, at least partial restoration of numbers of catecholamine varicosities occurred in all hypothalamic areas in all three age groups. It is concluded that, following selective lesions induced by the neurotoxin 6-OH-DA, catecholamine varicosities were restored both in immature and mature groups. According to the evidence obtained experimentally, the rate of restoration was greater in the neonate group, whereas the percentage restoration attained varies according to the hypothalamic area studied and the age of the animal. 相似文献
95.
K J Hwang 《Analytical biochemistry》1976,75(1):40-44
The influences of ATP and trichloroacetic acid on the color development of molybdenum blue in the Fiske and Subbarow method for the determination of inorganic phosphate were investigated. From these results optimum concentrations of ATP and trichloroacetic acid were recommended. Satisfactory results were obtained in the determination of the ATPase activity of sarcoplasmic reticulum membranes isolated from rabbit skeletal muscle. 相似文献
96.
Summary A population of nerve fibres in the gastro-intestinal tract of mice showing a high affinity for quinacrine was revealed by fluorescence microscopy. Similar results were obtained in rats and guinea pigs. Whole-mounts of sheets of the smooth muscle layer following incubation in 10-6-10-7 M quinacrine for 15–60 min revealed fine fluorescent varicose nerve fibers in the myenteric plexus of Auerbach both around nerve cell bodies and in the interconnecting strands. Many fibers were also present between the strands of the plexus, especially running parallel to the circular muscle layer. Such fibers were not seen in similarly quinacrine-incubated irides. A proportion of the cell bodies in Auerbach's plexus also showed quinacrine accumulation. These cells were apparently smaller neurons, sometimes with fluorescent processes. Intraperitoneal injections of quinacrine failed to demonstrate nerve fibers, but some cell bodies in Auerbach's plexus were positive. Subsequent paraformaldehyde treatment for monoamine visualization showed persistent adrenergic nerve terminals in the intestine and iris. These nerves seemed to be fewer and had a more yellow fluorescence than normally. The identity of the quinacrine-positive fibers is discussed with respect to recent suggestions that purinergic, substance P, enkephalin, and somatosin-containing nerves, in addition to adrenergic and cholinergic nerves, are present in the gut wall.Supported by the Swedish Medical Research Council (04X-03185). Magnus Bergvalls Stiftelse and Karolinska Institutets Fonder. For generous gifts of Mepacrine we thank Winthrop, Skärholmen, Stockholm, Sweden. The skilful technical assistance of Miss Gerd Boetius and Miss Maud Eriksson is gratefully acknowledged 相似文献
97.
Isolation and Genetic Analysis of Mutant Strains of CHLAMYDOMONAS REINHARDI Defective in Gametic Differentiation 总被引:1,自引:0,他引:1
Impotent mutant strains of Chlamydomonas reinhardi, mating-type (mt) plus, are described that have normal growth and motility but fail to differentiate into normal gametes. Procedures for their isolation and their genetic analysis are described. Five of the imp strains (imp-2, imp-5, imp-l, imp-7, and imp-8) exhibit no flagellar agglutination when mixed with mt- or mt+ gametes and the mutations are shown to be unlinked to the mt locus (with the possible exception of imp-7). Two of the strains (imp-3 and imp-4) carry leaky mutations that affect cell fusion; neither mutation is found by tetrad analysis to be linked to mt or to the other. Cells of the imp-1 strain agglutinate well with mt- gametes and active agglutination continues for up to 48 hours, but cell fusion occurs only very rarely. Analysis of these rare zygotes indicates that imp-1 is closely linked to the mt+ locus, and fine-structural studies reveal that imp-1 gametes produce a mutant mating structure involved in zygotic cell fusion. The development of sexuality in C. reinhardi therefore appears amenable to genetic dissection. 相似文献
98.
After 18 months of storage at -150 C, some larvae of Ditylenchus dipsaci, which had been treated in a 7.5% solution of dimethyl sulphoxide and cooled to -25 C before storage, were still viable on thawing. Some survivors penetrated and developed normally in stems of alfalfa seedlings. Tests showed that active larvae could be frozen directly, thus eliminating the need to use the quiescent stage of this nematode previously thought necessary for successful storage at cryogenic temperatures. The method described is suitable for long-term storage of D. dipsaci and may, with slight modifications, be used to preserve other plant-parasitic nematodes. 相似文献
99.
The human health risk of soils contaminated with As, Pb, Cu, and Zn was evaluated based on pseudo-total concentrations of metal(loid)s, the physiologically based extraction test (PBET), and diffusive gradients in thin films (DGT). Non-carcinogenic (NCR) and carcinogenic (CR) risks exceeded the U.S. Environmental Protection Agency criteria under both the residential and non-residential scenarios. Human bioavailable concentrations (PBET) were much lower than pseudo-total concentrations. The Hazardous Index of NCR (HI (NCR)) for the PBET in the studied soils was 67% and 94% less than that for pseudo-total concentration, respectively, under the non-residential and residential scenarios. Similarly, CR for the PBET was also 65% and 93% less for the two soils. The concentration of metal(loid)s accumulated in the DGT resin was highly correlated with the PBET-extractable concentration (R2 > 0.649). Therefore, for both the CR and HI (NCR), the DGT-calculated risk was linearly related to the PBET-calculated risk for the studied soils under both scenarios. The results suggest that DGT uptake and PBET-extracted concentrations are good surrogates for risk estimation and that both J1 and J2 soils require remediation before their use for residential or non-residential purposes. 相似文献
100.
Munkhtugs Davaatseren Jin-Taek Hwang Jae Ho Park Myung-Sunny Kim Shuaiyu Wang Mi Jeong Sung 《PloS one》2014,9(7)
Allyl isothiocyanate (AITC) is a phytochemical found in cruciferous vegetables that has known chemopreventive and chemotherapeutic activities. Thus far, the antiangiogenic activity of AITC has not been reported in in vivo studies. Herein, we investigated the effect of AITC on angiogenesis and inflammation in a mouse model of colitis. Experimental colitis was induced in mice by administering 3% dextran sulfate sodium via drinking water. To monitor the activity of AITC in this model, we measured body weight, disease activity indices, histopathological scores, microvascular density, myeloperoxidase activity, F4/80 staining, inducible nitric oxide synthase (iNOS) expression, cyclooxygenase-2 (COX-2) expression, and vascular endothelial growth factor (VEGF)-A/VEGF receptor 2 (VEGFR2) expression in the mice. We found that AITC-treated mice showed less weight loss, fewer clinical signs of colitis, and longer colons than vehicle-treated mice. AITC treatment also significantly lessened the disruption of colonic architecture that is normally associated with colitis and repressed the microvascularization response. Further, AITC treatment reduced both leukocyte recruitment and macrophage infiltration into the inflamed colon, and the mechanism these activities involved repressing iNOS and COX-2 expression. Finally, AITC attenuated the expression of VEGF-A and VEGFR2. Thus, AITC may have potential application in treating conditions marked by inflammatory-driven angiogenesis and mucosal inflammation. 相似文献