全文获取类型
收费全文 | 3376篇 |
免费 | 342篇 |
国内免费 | 3篇 |
专业分类
3721篇 |
出版年
2021年 | 62篇 |
2020年 | 30篇 |
2019年 | 33篇 |
2018年 | 36篇 |
2017年 | 27篇 |
2016年 | 69篇 |
2015年 | 87篇 |
2014年 | 105篇 |
2013年 | 130篇 |
2012年 | 167篇 |
2011年 | 149篇 |
2010年 | 121篇 |
2009年 | 99篇 |
2008年 | 140篇 |
2007年 | 116篇 |
2006年 | 122篇 |
2005年 | 111篇 |
2004年 | 121篇 |
2003年 | 93篇 |
2002年 | 120篇 |
2001年 | 83篇 |
2000年 | 89篇 |
1999年 | 88篇 |
1998年 | 44篇 |
1997年 | 46篇 |
1996年 | 40篇 |
1995年 | 39篇 |
1994年 | 35篇 |
1993年 | 43篇 |
1992年 | 57篇 |
1991年 | 60篇 |
1990年 | 62篇 |
1989年 | 62篇 |
1988年 | 49篇 |
1987年 | 51篇 |
1986年 | 61篇 |
1985年 | 62篇 |
1984年 | 43篇 |
1983年 | 31篇 |
1982年 | 28篇 |
1981年 | 26篇 |
1980年 | 41篇 |
1979年 | 50篇 |
1978年 | 32篇 |
1976年 | 33篇 |
1975年 | 36篇 |
1974年 | 30篇 |
1973年 | 42篇 |
1972年 | 35篇 |
1970年 | 29篇 |
排序方式: 共有3721条查询结果,搜索用时 0 毫秒
91.
The chemistry of the collagen cross-links. Characterization of the products of reduction of skin, tendon and bone with sodium cyanoborohydride. 下载免费PDF全文
Reduction of tissues with sodium cyanoborohydride at pH7.4 gave results identical with those obtained by KBH4 treatment. On reduction with sodium cyanoborohydride at pH 4.4, however, a previously undetected basic compound was formed and was identified by mass spectrometry and chemical degradation techniques as dihydrohydroxymerodesmosine. Histidino-hydroxymerodesmosine was not present, and further analysis confirmed that reduced aldol, a mojor product of reduction with KBH4 at the lower pH, was also absent. These results, together with an analysis of the time course of the reduction, support previous assertions that histidino-hydroxymerodesmosine is an artifact [robins *Bailey (1973) Biochem. J. 135, 657-665] and suggests that the non-reduced form of hydroxymerodesmosine probably does not constitute a major intermolecular bond in vivo. 相似文献
92.
Summary LW13K2 cells, a clone of a spontaneously in vitro transformed derivative of embryonic Lewis rat fibroblastic cells, were studied by phase contrast cine-light microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The ruffles found at the advancing edge of cells grown on glass substrates in vitro form and recede in a period of less than one min if they do not make an attachment of the substrate. If they fail to make an attachment they may form pinocytotic channels near the leading edge as described by Price (1972) and/or collapse, generally backwards, towards the cell body. The spines which appear to reinforce the membranous ruffles are the last structures to disappear, and accumulate in an irregular array behind the ruffling edge; this area is behind that in which pinocytosis occurs. In comparison with the sparse numbers of ribosomes found in the trailing edge, they are present in notable concentrations near the leading, ruffling edge of the cell. No membrane vesicles have been found in or near the ruffling edges at the ruffle-spine concentration zone. 相似文献
93.
94.
95.
An objective index of inhaling cigarette smoke based on carboxyhaemoglobin concentrations and the carbon monoxide yields of cigarettes was used to investigate possible systematic differences in the extent of inhaling among light and heavy smokers when classified according to their self described inhaling habits. A total of 2108 men who smoked cigarettes were studied. Heavy smokers (20 or more cigarettes a day) had a higher average inhaling index than light smokers (fewer than 20 cigarettes a day) both among those who said that they inhaled and among those who said that they did not. This observation, together with indirect evidence that heavy smokers who inhale deeply may to some extent avoid depositing smoke condensate on their main bronchial epithelium, explains a hitherto unresolved anomaly--namely, that the risk of lung cancer is less among heavy cigarette smokers who say that they inhale than it is among those who say that they do not inhale. 相似文献
96.
J M Lord S I White C J Bailey T W Atkins R F Fletcher K G Taylor 《BMJ (Clinical research ed.)》1983,286(6368):830-831
To investigate the effect of metformin on insulin receptor binding and diabetic control, eight obese type II diabetic patients were studied before treatment, after one and four weeks of taking metformin (500 mg thrice daily), and four weeks after withdrawal of the drug. After one and four weeks of treatment the number of erythrocyte insulin receptors had increased by 116% and 184% respectively. This was due almost entirely to an increase in the number of low affinity binding sites. The number of receptors was still raised four weeks after metformin had been withdrawn. Diabetic control as assessed by urinary glucose, glycosylated haemoglobin (HbA1), and glucose tolerance values was significantly improved during metformin treatment, while plasma insulin concentrations were not altered. These results indicate that metformin produces a rapid and protracted increase in low affinity insulin receptors in type II diabetes, associated with greater insulin sensitivity and improved diabetic control. 相似文献
97.
Enzymes are often immobilized on the internal surfaces of porous solid by immersing enzyme-free particles in a well mixed solution of enzyme. The ensuing impregnation process involves coupled transient mass transfer and surface attachment of enzyme. A mathematical model is employed to explore the influences of process parameters on the amount of enzyme loaded and the distribution of immobilized enzyme within the support particles. Nonuniform loading of the support occurs under some conditions. This is significant since the distribution of enzyme within the support particle influences the overall activity and stability of the immobilized enzyme catalyst. The model developed here may also be used to describe removal of reversibly immobilized enzyme during washing or utilization of the immobilized enzyme catalyst. 相似文献
98.
A review of the salt sensitivity of the Australian freshwater biota 总被引:13,自引:7,他引:6
Barry T. Hart Paul Bailey Rick Edwards Kent Hortle Kim James Andrew McMahon Charles Meredith Kerrie Swadling 《Hydrobiologia》1991,210(1-2):105-144
In Victoria, Australia, both dryland salinity and salinity in irrigation regions are serious agricultural problems. One option
to control the latter is to pump groundwater to maintain it below the surface. However, this leaves a saline wastewater for
disposal, probably into local streams or wetlands. This review of the salt sensitivity of the biota of Australian streams
and wetlands gives information of interest to those responsible for developing controls on these discharges. The review addresses
the lethal and sub-lethal effects of salinity on microbes (mainly bacteria), macrophytes and micro-algae, riparian vegetation,
invertebrates, fish, amphibians, reptiles, mammals, and birds. Data suggest that direct adverse biological effects are likely
to occur in Australian river, stream and wetland ecosystems if salinity is increased to around 1 000 mg L−1. The review highlights a general lack of data on the sensitivity of freshwater plants and animals to salinity increases. 相似文献
99.
100.
J. S. Bailey 《Plant and Soil》1992,143(1):19-31
Solution culture studies have shown that plant uptake of NH4
+ and NO3
- can be improved by increasing the concentration of Ca2+ in the root environment: the same may be true for grass grown in soil culture. An experiment was set up to see whether gypsum (CaSO4 2H2O) increased the rate at which perennial ryegrass absorbed 15NH4
+ and 15NO3
- from soil.The results demonstrated that gypsum increases the rates of uptake of both NH4
+ and NO3
- by perennial ryegrass. However because there was little potential for mineral-N loss from the experimental system, either by gaseous emission or by N immobilization, long term improvements in fertilizer efficiency were not observed. Nitrogen cycling from shoots to roots commenced once net uptake of N into plants had ceased. Labelled N transferred thus to roots underwent isotopic exchange with unlabelled soil N. It was suggested that this exchange of N might constitute an energy drain from the plant, if plant organic N was exchanged for soil inorganic N. The fact that the exchange occurred at all cast doubt on the suitability of the 15N-isotope dilution technique for assessing fertilizer efficiency in medium to long term experiments. There was evidence that the extra NO3
--N taken up by plants on the all-nitrate treatments as a result of gypsum application, was reduced in root tissue rather than in shoots, but to the detriment of subsequent root growth and N uptake. 相似文献