全文获取类型
收费全文 | 548篇 |
免费 | 66篇 |
专业分类
614篇 |
出版年
2022年 | 5篇 |
2021年 | 7篇 |
2019年 | 7篇 |
2018年 | 11篇 |
2017年 | 5篇 |
2016年 | 11篇 |
2015年 | 17篇 |
2014年 | 20篇 |
2013年 | 18篇 |
2012年 | 22篇 |
2011年 | 29篇 |
2010年 | 17篇 |
2009年 | 13篇 |
2008年 | 24篇 |
2007年 | 16篇 |
2006年 | 24篇 |
2005年 | 18篇 |
2004年 | 20篇 |
2003年 | 19篇 |
2002年 | 20篇 |
2001年 | 8篇 |
2000年 | 16篇 |
1999年 | 9篇 |
1998年 | 5篇 |
1997年 | 6篇 |
1995年 | 9篇 |
1994年 | 8篇 |
1993年 | 7篇 |
1992年 | 10篇 |
1991年 | 9篇 |
1990年 | 10篇 |
1989年 | 16篇 |
1988年 | 11篇 |
1987年 | 8篇 |
1986年 | 6篇 |
1985年 | 9篇 |
1984年 | 15篇 |
1983年 | 11篇 |
1982年 | 8篇 |
1981年 | 7篇 |
1980年 | 5篇 |
1979年 | 8篇 |
1978年 | 7篇 |
1977年 | 7篇 |
1976年 | 8篇 |
1975年 | 12篇 |
1973年 | 7篇 |
1970年 | 8篇 |
1967年 | 4篇 |
1965年 | 7篇 |
排序方式: 共有614条查询结果,搜索用时 15 毫秒
1.
Theodore Page Charles Sherwood James D. Connor Thomas Tarnowski 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1996,675(2):342
A fast, simple, and cost-effective HPLC method for the quantitation of the antiviral drug ganciclovir is described. The serum samples are extracted with perchloric acid and neutralized with potassium phosphate buffer, and urine samples are diluted with distilled water. A reversed-phase column with isocratic elution by 15 mM potassium phosphate buffer (pH 2.5) containing 0.25% acetonitrile is used to separate ganciclovir; quantitation is by UV absorbance at 254 nm. Total turnaround time is 22 min; more than 3000 samples can be run on a single column without loss of peak quality. The limit of quantitation is 0.05 μg/ml. Recoveries varied from 91 to 10% with coefficients of variation ranging from 0.387 to 7.95%. 相似文献
2.
Effect of cycloheximide on development of methotrexate resistance of Chinese hamster ovary cells treated with inhibitors of DNA synthesis. 总被引:8,自引:0,他引:8
We examined the effects of 18 h of incubation of Chinese hamster ovary (CHO K1) cells with cycloheximide, hydroxyurea, and aphidicolin. Treatment of cells with cycloheximide alone at a concentration adequate to inhibit DNA synthesis to less than 10% of control was significantly less cytotoxic and clastogenic than treatment with hydroxyurea or aphidicolin, did not induce unbalanced cellular growth, and had no effect on the frequency of resistant cells in methotrexate selections compared with control cells. When combined with hydroxyurea or aphidicolin and compared with the effects of either drug alone, cycloheximide blocked the induction of unbalanced growth during drug treatment, reduced the frequency of chromosomal aberrations in recovering cell populations, and decreased cell killing. In addition, the increased frequency of methotrexate-resistant cells observed after treatment with hydroxyurea or aphidicolin was eliminated when cycloheximide was present during drug treatment. 相似文献
3.
DNA-binding properties of the Drosophila melanogaster zeste gene product. 总被引:17,自引:1,他引:16 下载免费PDF全文
A Mansukhani A Crickmore P W Sherwood M L Goldberg 《Molecular and cellular biology》1988,8(2):615-623
4.
Amos Banin Glenn C. Carle Sherwood Chang Lelia M. Coyne James B. Orenberg Thomas W. Scattergood 《Origins of life and evolution of the biosphere》1988,18(3):239-265
Two major questions have been raised by prior explorations of Mars. Has there ever been abundant water on Mars? Why is the iron found in the Martian soil not readily seen in the reflectance spectra of the surface? The work reported here describes a model soil system of Mars Soil Analog Materials, MarSAM, with attributes which could help resolve both of these dilemmas. The first set of MarSAM consisted of a suite of variably iron/calcium-exchanged montmorillonite clays. Several properties, including chemical composition, surface-ion composition, water adsorption isotherms, and reflectance spectra, of these clays have been examined. Also, simulations of the Viking Labeled Release Experiment using the MarSAM were performed. The results of these studies show that surface iron and adsorbed water are important determinants of clay behavior as evidenced by changes in reflectance, water absorption, and clay surface reactions. Thus, these materials provide a model soil system which reasonably satisfies the constraints imposed by the Viking analyses and remote spectral observations of the Martian surface, and which offers a sink for significant amounts of water. Finally, our initial results may provide insights into the mechanisms of reactions that occur on clay surfaces as well as a more specific approach to determining the mineralogy of Martian soils. 相似文献
5.
M R Vaupel O D Sherwood M B Anderson 《The journal of histochemistry and cytochemistry》1985,33(4):303-308
Immunocytochemical staining for relaxin in ovarian sections of pregnant mice from day 11 through day 18 of gestation revealed that only corpora lutea (CL) of pregnancy are stained. Evaluation of serial sections of ovaries from a day 16 pregnant mouse revealed that the only luteal structures present are CL of pregnancy. The number of CL present in each ovary equaled the number of implantation sites in each related horn (7 on the right side and 8 on the left side). These large CL varied in shape, being round in some profiles to very elongate in others. All CL were immunochemically stained for relaxin using the peroxidase-antiperoxidase method of L. Sternberger (Immunocytochemistry, 2nd ed. Wiley, New York, 1979). The intensity of the strain varied from cell to cell within each CL. Small luteal structures that were observed to be immunochemically stained for relaxin were demonstrated to represent the periphery of CL of pregnancy. No luteinized follicles were observed and interstitial cells and follicles were not immunochemically stained in any of the day 16 serial ovarian sections or in any of the ovarian sections from pregnant mice on the other days of gestation studied. CL of previous cycles were not observed to be present in the ovaries at days 15, 16, or 18 of gestation. However on day 14 and before, CL of previous cycles were observed and they did not exhibit any relaxin immunostaining. Immunocytochemical studies using the biotin-avidin system revealed that no relaxin immunostaining could be demonstrated in the ovaries of cycling mice at any stage of the estrous cycle. In conclusion, this study revealed that the only ovarian structures demonstrating relaxin immunocytochemical staining in the mouse were CL of pregnancy. 相似文献
6.
Allan K. Stobart W. Trevor Griffiths Ibraheem Ameen-Bukhari Robert P. Sherwood 《Physiologia plantarum》1985,63(3):293-298
The effect of cadmium on the biosynthesis of chlorophyll has been investigated in the leaves of dark-grown seedlings of barley ( Hordeum vulture L. cv. Proctor). Cd2+ inhibited the production of chlorophyll by affecting 1) the synthesis of 5-aminolacvulinic acid and 2) the protoehlorophyllide reductase ternary complex with its substrates. Cd2+ had no effect on the constituent enzymes that catalyse the synthesis of free protoehlorophyllide from 5-aminolaevulinic acid. The results obtained are consistent with Cd2+ inhibiting the formation of chlorophyll by reacting with essential thiol groups in both the protochlorophyllide reductase protein and the enzyme(s) involved in the light dependent synthesis of 5-aminolaevulinic acid. 相似文献
7.
Additional Restriction Endonuclease Cleavage Sites on the Bacteriophage P22 Genome 总被引:7,自引:0,他引:7 下载免费PDF全文
We present complete restriction endonuclease cleavage site maps of the bacteriophage P22 chromosome for 16 enzymes with six base recognition sequences, thereby positioning 116 new sites on the chromosome. Twenty-four such restriction maps for P22 DNA, containing 162 sites, have now been completed, and three enzymes were found that did not cut P22 DNA. Our results are consistent with the ideas that ClaI does not cleave the methylated recognition sequence ATCGA(me)T or A(me)TCGAT and StuI does not cleave the methylated recognition sequence AGGCC(me)T. 相似文献
8.
Fed batch experiments were performed to test the effects of electron donor and electron acceptor availability on the production of chloroform (CF) during carbon tetrachloride (CT) destruction by a denitrifying bacterial consortium. In one series of tests, acetate (electron donor) was present in excess while nitrate and nitrite (electron acceptor) were limiting. In the other series of tests, acetate was the limiting nutrient, and nitrate and nitrite were in excess. Under nitrate limiting conditions, 50% (+/-17%) of the CT transformed by the microorganisms was converted to CF. However, under acetate limiting conditions, only 4% (+/-4%) of the CT that was degraded appeared as CF. Previous research had suggested that denitrifying bacteria can degrade CT via two competing pathways. One of these pathways produces CF as the predominant end product. The second pathway produces CO(2) as the primary end product. The results shown here suggest that the first pathway is dominant when nitrate and nitrite are depleted while the second pathway, which produces little CF, dominates when nitrate or nitrite are available. 相似文献
9.
Cell extracts of Fibrobacter succinogenes subsp. succinogenes S85 phosphorylated glucose with a GTP-dependent glucokinase. The enzyme showed little activity with ATP (12% of that with GTP). Of other phosphate donors tested, only dGTP and ITP gave high glucokinase activities. Dialyzed extracts required Mg+2 and K+ for maximal activity. In potassium phosphate buffer, glucokinase showed maximum activity at pH 7.5 with glucose-6-phosphate dehydrogenase as the coupling enzyme. In this assay, glucokinase was active with glucose (100%), 2-deoxy-d-glucose (40%), and mannose (20%). Partially purified glucokinase had a molecular weight of 82,000 and a pl of 4.82. Double-reciprocal plots of substrate concentration versus velocity were linear and the enzyme had apparent Km values of 55 M for glucose and 72 M for GTP. Dialyzed cell extracts of Fibrobacter intestinalis C1A also contained a GTP-dependent glucokinase that showed little activity with ATP. Potassium also stimulated the activity of this enzyme. These results suggest that this unusual glucokinase may be characteristic of the genus Fibrobacter.Abbreviations
CHES
cyclohexylaminoethanesulfonic acid
-
GK
glucokinase
-
PEP
phosphoenolpyruvate
Published with the approval of the Director of the North Dakota Agricultural Experiment Station as journal article no. 2186 相似文献
10.