全文获取类型
收费全文 | 2566篇 |
免费 | 215篇 |
国内免费 | 4篇 |
出版年
2021年 | 31篇 |
2020年 | 17篇 |
2019年 | 35篇 |
2018年 | 28篇 |
2017年 | 21篇 |
2016年 | 50篇 |
2015年 | 65篇 |
2014年 | 106篇 |
2013年 | 105篇 |
2012年 | 160篇 |
2011年 | 161篇 |
2010年 | 103篇 |
2009年 | 99篇 |
2008年 | 138篇 |
2007年 | 140篇 |
2006年 | 141篇 |
2005年 | 137篇 |
2004年 | 156篇 |
2003年 | 124篇 |
2002年 | 150篇 |
2001年 | 25篇 |
2000年 | 16篇 |
1999年 | 32篇 |
1998年 | 28篇 |
1997年 | 31篇 |
1996年 | 28篇 |
1995年 | 26篇 |
1994年 | 22篇 |
1993年 | 28篇 |
1992年 | 29篇 |
1991年 | 25篇 |
1990年 | 17篇 |
1989年 | 21篇 |
1988年 | 19篇 |
1987年 | 20篇 |
1986年 | 19篇 |
1985年 | 16篇 |
1984年 | 29篇 |
1983年 | 24篇 |
1982年 | 31篇 |
1981年 | 46篇 |
1980年 | 27篇 |
1979年 | 23篇 |
1978年 | 25篇 |
1977年 | 23篇 |
1976年 | 24篇 |
1975年 | 26篇 |
1974年 | 19篇 |
1973年 | 20篇 |
1971年 | 14篇 |
排序方式: 共有2785条查询结果,搜索用时 15 毫秒
31.
Esmail K. Shubber David Jacobson-Kram Dr. Jerry R. Williams 《Cell biology and toxicology》1986,2(3):379-399
Seven antischistosomal drugs, two antimalarial drugs, and one antiamoebic drug were tested in all five Ames strains for induction of mutation, as well as for induction of cytotoxicity, inhibition of cellular progression, and the induction of sister chromatid exchanges in two cultured mammalian cell lines. We found that two agents shown to be negative in the Ames test were positive for sister chromatid exchange induction. Based on qualitative and quantitative evaluation, we find that all but three of the pharmaceuticals should be considered to be potential human carcinogens.Abbreviations AA
2-aminoanthracene
- 9AACC
9-aminoacridine
- AM
amoscanate
- BrdUU
bromodeoxyuridine
- CA
chloroquine diphosphate
- CHO
Chinese hamster ovary
- CQ
chloroquine
- DAPI
46-diamidino-2-phenylindole
- DHY
dehydroemetine
- DMSO
dimethyl sulfoxide
- EB
ethidium bromide
- FCS
fetal calf serum
- FN
4-fluoro-3-nitrophenyl azide
- HY
hycanthone
- ICP
inhibiting cell progression
- LU
lucanthone
- MEM
minimal essential medium
- 2NF
2-nitrofurantoin
- 4NPD
4-nitro-O-phenylenediamine
- NZ
niridazole
- OL
oltipraz
- OX
oxaminiquine
- PBS
phosphate buffered saline
- PQ
primaquine
- PZ
praziquantel
- SA
sodium azide
- SCE
sister chromatid exchange 相似文献
32.
Jerry R. Colca Nirmala Kotagal Paul E. Lacy Michael L. McDaniel 《生物化学与生物物理学报:生物膜》1983,729(2):176-184
The properties of active or ATP-dependent calcium transport by islet-cell endoplasmic reticulum and plasma membrane-enriched subcellular fractions were directly compared. These studies indicate that the active calcium transport systems of the two membranes are fundamentally distinct. In contrast to calcium uptake by the endoplasmic reticulum-enriched fraction, calcium uptake by islet-cell plasma membrane-enriched vesicles exhibited a different pH optimum, was not sustained by oxalate, and showed an approximate 30-fold greater affinity for ionized calcium. A similar difference in affinity for calcium was exhibited by the Ca2+-stimulated ATPase activities which are associated with these islet-cell subcellular fractions. Consistent with the effects of calmodulin on calcium transport, calmodulin stimulated Ca2+-ATPase in the plasma membranes, but did not increase calcium-stimulated ATPase activity in the endoplasmic reticulum membranes. The physiological significance of the differences observed in calcium transport by the endoplasmic reticulum and plasma membrane fractions relative to the regulation of insulin secretion by the islets of Langerhans is discussed. 相似文献
33.
Constantin Cojocel Keizo Maita Dale A. Pasino Chao-Hen Kuo Jerry B. Hook 《Life sciences》1983,33(9):855-861
Proximal and distal tubule suspensions were prepared from kidneys of Sprague-Dawley rats by an isolation procedure on a PercollR gradient. The marker enzymes alkaline phosphatase (brush border) and hexokinase (cytoplasmic) as well as p-aminohippurate transport capacity, gluconeogenic activity and electron microscopy were used to characterize the two kidney tubule suspensions. The results of this study indicate that cytochrome P-450 is localized to the proximal tubular cells and that the O-deethylation of 7- ethoxycoumarin was higher in the proximal than distal fraction. Both proximal and distal tubules showed glucuronidation and deacetylation capacities and a relatively equal distribution of non-protein sulfhydryls. These studies demonstrate metabolic heterogeneity of the nephron, the proximal tubule being the main site of renal xenobiotic metabolism. Understanding of metabolic heterogeneity of proximal and distal kidney tubules should provide important information regarding cell specific mechanisms of nephrotoxicity. 相似文献
34.
The effect of grazing on primary productivity and phosphorus cycling in autotrophic streams was studied using the snail Goniobasis clavaeformes. Snails were added to each of three replicate laboratory stream channels, receiving once-through flow of groundwater, in densities of 2.1, 3.0, and 4.2 g ash free dry mass (AFDM)/m2. A fourth channel received no snails and served as an ungrazed control. Presence of snail grazers resulted in a large reduction in aufwuchs biomass, primary productivity, and biotic phosphorus uptake; a modest reduction in fine particulate organic matter (FPOM); and an increase in the fraction of stream particulate organic matter (POM) exported as seston. Although primary production and aufwuchs biomass continued to decline with increasing snail density, phosphorus uptake increased. This increased phosphorus uptake is attributed to abiotic sorption to inorganic surfaces exposed as a result of efficient removal of aufwuchs at high snail densities. Although snail densities were chosen to bracket the density measured in a natural stream, the experimental densities may result in considerably higher grazing pressure on aufwuchs due to the absence of alternate food sources (e.g., coarse particulate organic matter) usually found in natural streams. Presence of snail grazers increased the spiralling length of phosphorus, primarily by reducing aufwuchs biomass and consequently reducing uptake of phosphorus from the water. Presence of snails also increased downstream transport velocity of phosphorus bound to organic particles. These results follow the patterns predicted in a previous theoretical analysis for mildly phosphorus-limited streams. 相似文献
35.
13C NMR resonances of 15 simple tetrahydroisoquinolines have been assigned on the basis of chemical shift theory, 13C-1H coupling constants 相似文献
36.
Jerry L. Phillips Stephanie Waddingham Deborah A. Spiva 《Biological trace element research》1983,5(1):47-53
Lymphocytes were obtained from two patients with paroxysmal nocturnal hemoglobinuria as well as from apparently healthy controls and from patients with acute lymphoblastic leukemia and chronic lymphocytic leukemia. Subsequently, several aspects of zinc metabolism were studied in vitro in short-term cultures of these lymphocytes in order to assess lymphocyte functional capacity. The results of mitogen stimulation and zinc uptake studies for lymphocytes from donors with paroxysmal nocturnal hemoglobinuria were similar to those obtained for leukemic lymphocytes. The results of studies to determine the inducibility of the low molecular weight zinc-binding protein, metallothionein, by zinc were complicated by the decrease in overall protein synthesis in lymphocytes from donors in the paroxysmal nocturnal hemoglobinuria. It is proposed that paroxysmal nocturnal hemoglobinuria is indeed a clonal disorder and the relationship between lymphocytes in this disorder and leukemic lymphocytes is discussed. 相似文献
37.
38.
The applicability of two methods (pyrolysis gas chromatography and acidification-wet oxidation) for determining14CO2 incorporation into soil microorganisms was investigated. Both methods were able to distinguish biologically incorporated14C from abiotically adsorbed14C, but to varying degrees, there being a larger carryover of abiotic14C into the organic fraction and a higher percentage of assimilated14C in the organic fraction with the wet oxidation method. Using14C assimilation as a measure, it was possible to determine microbial activities in soils of diverse properties under a variety
of conditions, including polar soils under harsh environmental conditions. Both light and dark14CO2 fixation was measurable.14CO2 assimilation was not always proportional to the enumerable microorganisms. A new design for measurement of microbial activityin situ enabled measurement of total C influx (primary productivity) into soils with minimal perturbation to the natural soil ecosystem. 相似文献
39.
40.
Evaluation of Factors Related to Growth of Rift Valley Fever Virus in Suspended Cell Cultures 总被引:2,自引:2,他引:0 下载免费PDF全文
Jerry S. Walker Richard C. Carter Frederick Klein Shirley E. Snowden Ralph E. Lincoln 《Applied microbiology》1969,17(5):658-664
The effect of several controlled variables on the peak titer and fold increase of Rift Valley fever virus grown in suspension culture on two variants of Earle's L cell, L-DR and L-MA clone 1-1, was studied. No significant amount of cell-associated virus was found at 24 hr, indicating a release of virus soon after its formation. Mild sonic treatment of the virus produced in serum-free medium increased the infective titer about 10x. This difference was not observed with virus produced in medium supplemented with serum. Peak titer was not affected by medium used during the infection period, by multiplicity of inoculum (MOI), or by initial cell concentration within the test range of 10(4) to 2 x 10(6) cell/ml. Cell strain employed influenced titer, because the L-DR cell did not produce virus efficiently at low MOI and low initial cell concentration. The time of peak titer and fold replication was dependent on MOI and initial cell concentration. Differences in virus propagation in monolayer and suspension systems are discussed. 相似文献