全文获取类型
收费全文 | 3139篇 |
免费 | 260篇 |
出版年
2023年 | 12篇 |
2022年 | 45篇 |
2021年 | 83篇 |
2020年 | 40篇 |
2019年 | 53篇 |
2018年 | 57篇 |
2017年 | 51篇 |
2016年 | 71篇 |
2015年 | 134篇 |
2014年 | 171篇 |
2013年 | 197篇 |
2012年 | 266篇 |
2011年 | 272篇 |
2010年 | 163篇 |
2009年 | 145篇 |
2008年 | 154篇 |
2007年 | 158篇 |
2006年 | 109篇 |
2005年 | 132篇 |
2004年 | 132篇 |
2003年 | 101篇 |
2002年 | 110篇 |
2001年 | 41篇 |
2000年 | 43篇 |
1999年 | 45篇 |
1998年 | 40篇 |
1997年 | 17篇 |
1996年 | 23篇 |
1995年 | 30篇 |
1994年 | 17篇 |
1993年 | 20篇 |
1992年 | 28篇 |
1991年 | 16篇 |
1990年 | 14篇 |
1989年 | 19篇 |
1988年 | 13篇 |
1987年 | 14篇 |
1985年 | 15篇 |
1984年 | 23篇 |
1983年 | 18篇 |
1982年 | 15篇 |
1981年 | 15篇 |
1980年 | 17篇 |
1979年 | 17篇 |
1978年 | 13篇 |
1977年 | 12篇 |
1974年 | 13篇 |
1973年 | 12篇 |
1970年 | 15篇 |
1969年 | 10篇 |
排序方式: 共有3399条查询结果,搜索用时 15 毫秒
21.
J. L. Burton W. J. Cunliffe D. G. Millar Sam Shuster 《BMJ (Clinical research ed.)》1970,2(5712):769-771
Sebum excretion rates from forehead skin were measured serially during and after pregnancy in 10 normal women. Only minor fluctuations occurred during the middle and last trimesters of pregnancy, but there was a pronounced decrease in the postpartum period. Probably a powerful sebotrophic factor is present in pregnancy, but its nature is conjectural. 相似文献
22.
23.
Laszlo Ambrus Sam H. Thal Selig B. Weinstein Juanita Warnecke 《The Western journal of medicine》1967,106(5):354-358
Following a six-week program of training in a series of exercises, a significant number of patients with chronic obstructive pulmonary emphysema showed decided improvement in functional activity. Subjective improvement also was noted and kept the patient motivation high.Preliminary observations indicated that the improvement could be maintained long after the end of the training period. 相似文献
24.
25.
26.
Mechanism of cadmium uptake by activated sludge 总被引:2,自引:0,他引:2
Rémy Gourdon Emilia Rus Shubhangi Bhende Sam S. Sofer 《Applied microbiology and biotechnology》1990,34(2):274-278
Summary The significance of metabolic activity in cadmium uptake by unacclimated activated sludge was studied. Below 30 mg/l cadmium in solution, biosorption was found to follow the Freundlich isotherm, which is the most common pattern for physico-chemical adsorption. More than 95% of total cadmium uptake was achieved within 5 min metal-sludge contact time. Biosorption increased strongly when the initial cadmium concentration in solution was raised from 10 to 100 mg/l, whereas in the same concentration range the metabolic activity of the sludge, as measured by respiratory activity and extracellular protein production, was very significantly inhibited. The addition of nutrients at low but significant levels failed to increase cadmium uptake in 2 h contact time, while in 24 h the addition of nutrients caused the biosorption to increase by only 5–10% without any significant growth of the biomass. Biosorption was found to increase with temperature between 5° C and 40° C, in correlation with an increase in the metabolic activity of the sludge. Pretreatment of the sludge with metabolic inhibitors (NaN3 and UV rays) appeared to cause only a very slight decrease (5–10%) of biosorption. These results suggest that metabolic uptake of cadmium was low and that adsorption to the surface of the cells was the major mechanism of uptake.Offprint requests to: S. S. Sofer 相似文献
27.
The effectiveness of two commonly used preservatives, sodium benzoate and potassium disulfite, was evaluated in terms of their
bactericidal activity and capacity to induce changes in the surface properties ofEscherichia coli isolated from commercial food preserves. Preservative treatment over a five-week test period resulted in controlling the
multiplication of these organisms and causing a decline in cell-surface hydrophobicity, hemagglutinating ability and adherence
capacity to rat intestinal cells ofE. coli isolates. A loss in motility was also exhibited. 相似文献
28.
J. N. Galloway R. W. Howarth A. F. Michaels S. W. Nixon J. M. Prospero F. J. Dentener 《Biogeochemistry》1996,35(1):3-25
Anthropogenic food and energy production extensively mobilize reactive nitrogen (N) in the watershed of the North Atlantic Ocean (NAO). There is wide spread N distribution by both hydrologic and atmospheric processes within the watershed of the NAO, resulting in reactive N accumulation in terrestrial systems. Net denitrification in most estuaries and continental shelves exceeds the amount of N supplied to the shelves by rivers and requires a supply of nitrate from the open ocean. Thus riverine N is only transported to the open ocean in a few areas with the flow from a few major rivers (e.g., Amazon). Atmospheric N deposition to the open ocean has increased and may increase the productivity of the surface ocean. In addition, as a consequence of increased Fe deposition to the open ocean (due in part to anthropogenic processes), the rate of biological N-fixation may have increased resulting in N accumulation in the ocean. Phosphorus (P) is also mobilized by anthropogenic processes (primarily food production). Relative to N, more of the P is transported across the shelf to the open ocean from both estuaries and major rivers. There are several consequences of the increased availability of N and P that are unique to each element. However, the control on primary productivity in both coastal and open ocean ecosystems is dependent on a complex and poorly understood interaction between N and P mobilization and availability. 相似文献
29.
Ralph A. Nixon Susan E. Lewis Marc Mercken Ram K. Sihag 《Neurochemical research》1994,19(11):1445-1453
Newly synthesized neurofilament proteins become highly phosphorylated within axons. Within 2 days after intravitreously injecting normal adult mice with [32P]orthophosphate, we observed that neurofilaments along the entire length of optic axons were radiolabeled by a soluble32P-carrier that was axonally transported faster than neurofilaments.32P-incorporation into neurofilament proteins synthesized at the time of injection was comparatively low and minimally influenced the labeling pattern along axons.32P-incorporation into axonal neurofilaments was considerably higher in the middle region of the optic axons. This characteristic non-uniform distribution of radiolabel remained nearly unchanged for at least 22 days. During this interval, less than 10% of the total32P-labeled neurofilaments redistributed from the optic nerve to the optic tract. By contrast, newly synthesized neurofilaments were selectively pulse-labeled in ganglion cell bodies by intravitreous injection of [35S]methionine and about 60% of this pool translocated by slow axoplasmic transport to the optic tract during the same time interval. These findings indicate that the steady-state or resident pool of neurofilaments in axons is not identical to the newly synthesized neurofilament pool, the major portion of which moves at the slowest rate of axoplasmic transport. Taken together with earlier studies, these results support the idea that, depending in part on their phosphorylation state, transported neurofilaments can interact for short or very long periods with a stationary but dynamic neurofilament lattice in axons.Special issue dedicated to Dr. Sidney Ochs. 相似文献
30.
Jeffrey S. Chamberlain Michael Boehnke Thomas S. Frank Sam Kiousis Junxhe Xu Sun-Wei Guo Elizabeth R. Hauser Robert A. Norum Elizabeth A. Helmbold Dorene S. Markel Sima M. Keshavarzi C. Eugene Jackson Kathleen Calzone Judy Garber Francis S. Collins Barbara L. Weber 《American journal of human genetics》1993,52(4):792-798
Previous studies have demonstrated linkage between early-onset breast cancer and ovarian cancer and genetic markers on chromosome 17q21. These markers define the location of a gene (BRCA1) which appears to be inherited as an autosomal dominant susceptibility allele. We analyzed five families with multiple affected individuals for evidence of linkage to the BRCA1 region. Two of the five families appear to be linked to BRCA1. One apparently linked family contains critical recombinants, suggesting that the gene is proximal to the marker D17S579 (Mfd188). These findings are consistent with the maximum-likelihood position estimated by the Breast Cancer Linkage Consortium and with recombination events detected in other linked families. Linkage analysis was greatly aided by PCR-based analysis of paraffin-embedded normal breast tissue from deceased family members, demonstrating the feasibility and importance of this approach. One of the two families with evidence of linkage between breast cancer and genetic markers flanking BRCA1 represents the first such family of African-American descent to be reported in detail. 相似文献