首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   3938篇
  免费   368篇
  国内免费   1篇
  2022年   40篇
  2021年   89篇
  2020年   46篇
  2019年   59篇
  2018年   73篇
  2017年   47篇
  2016年   102篇
  2015年   188篇
  2014年   200篇
  2013年   248篇
  2012年   241篇
  2011年   265篇
  2010年   157篇
  2009年   125篇
  2008年   193篇
  2007年   200篇
  2006年   186篇
  2005年   188篇
  2004年   166篇
  2003年   138篇
  2002年   139篇
  2001年   63篇
  2000年   55篇
  1999年   55篇
  1998年   48篇
  1997年   32篇
  1996年   32篇
  1995年   29篇
  1994年   26篇
  1993年   32篇
  1992年   51篇
  1991年   39篇
  1990年   29篇
  1989年   37篇
  1988年   36篇
  1987年   23篇
  1985年   27篇
  1984年   28篇
  1983年   28篇
  1982年   33篇
  1981年   25篇
  1980年   34篇
  1979年   24篇
  1978年   26篇
  1977年   21篇
  1976年   20篇
  1975年   18篇
  1974年   23篇
  1973年   21篇
  1971年   26篇
排序方式: 共有4307条查询结果,搜索用时 0 毫秒
111.

Background, aim and scope  

Although life cycle assessment is frequently used in scientific studies of product comparison, many practitioners are looking for improvements in the normalisation, grouping and weighting of life cycle inventory results. Local conditions, which are well known to local experts, are very important to these steps. The goal of this work was to develop a computer-based decision support system for classifying wood products according to their influence on the environment in their whole life cycle. The model specifically addresses local conditions in the Republic of Slovenia and was developed by Slovenian experts.  相似文献   
112.
Details of a sensitive and specific radioimmunoassay for androsterone (1) and androsterone sulfate in plasma have been presented. Benzene extracts of plasma were chromatographed on a lumina to isolate the androsterone fraction either (a) directly after extraction (A) or (b) after solvolysis (AS). Following treatment with rabbit anti-A-17-BSA, antibody bound steroid was precipitated by ammonium sulfate. Androsterone concentrations in normal male plasma averaged 57 ± 24 (S.D.) ng/dl, range 35–135 ng/dl and for normal women, 44 ± 21 (S.D.) ng/dl, range 18–98 ng/dl. Androsterone sulfate concentrations were: males 55 ± 28 μg/dl (range 10–114 μg/dl); premenopausal females 52 ± 31 μg/dl (range 16–318 μg/dl).  相似文献   
113.
Early and late replicating chromosomal banding patterns of Gallus domesticus were investigated by cell synchronization and incorporation of 5'-bromodeoxyuridine during early and late DNA synthesis. The early replicating chromosomal banding patterns observed, as revealed by either acridine orange or Hoechst 33258/propidium iodide staining, were similar to the structural G-banding patterns obtained by trypsin digestion and Giemsa staining. Late replicating chromosomal banding showed extensive reverse band complementarity to the G-banding pattern. Cell synchronization increased the number of prometaphase and metaphase plates available for analysis. G-banding obtained by Hoechst 33258/propidium iodide staining was investigated due to the fact that it is compatible with chromosomal in situ hybridization procedures that use nonisotopically-labeled DNA probes. Standard replicative G-banded and R-banded idiograms, as obtained after cell synchronization, are proposed.  相似文献   
114.
115.
Unfertilized eggs and early embryos up to the 2-day (16-cell) cleavage stage of development in the rabbit contain predominantly the most cathodal lactate dehydrogenase isoenzyme made up of A-type subunits. Following early cleavage there is a progressing increase in total LDH activity in the embryo as development proceeds through 4- and 6-day blastocyst stages. This is accompanied by an increase in the amount of B-type subunits and a concomitant shift in the lactate dehydrogenase isoenzyme electrophoretic pattern toward the anodal isoenzyme types.  相似文献   
116.
117.
Biological fluid sample collection often includes the risk of blood contamination that may alter the proteomic profile of biological fluid. In proteomics studies, exclusion of contaminated samples is usually based on visual inspection and counting of red blood cells in the sample; analysis of specific blood derived proteins is less used. To fill the gap, we developed a fast and sensitive method for ascertainment of blood contamination in crude biological fluids, based on specific blood-derived protein, hemoglobin detection by MALDI-TOF MS. The MALDI-TOF MS based method allows detection of trace hemoglobin with the detection limit of 0.12 nM. UV-spectrometry, which was used as reference method, was found to be less sensitive. The main advantages of the presented method are that it is fast, effective, sensitive, requires very small sample amount and can be applied for detection of blood contamination in various biological fluids collected for proteomics studies. Method applicability was tested on human cerebrospinal and follicular fluid, which proteomes generally do not contain hemoglobin, however, which possess high risk for blood contamination. Present method successfully detected the blood contamination in 12 % of cerebrospinal fluid and 24 % of follicular fluid samples. High percentage of contaminated samples accentuates the need for initial inspection of proteomic samples to avoid incorrect results from blood proteome overlap.  相似文献   
118.
119.
The pistillate flowers of Arceuthobium show a high degree of uniformity and structural simplicity. Because of their simplicity certain structures such as the carpel and the placenta have been difficult to interpret. From this study, the placenta is interpreted as a composite structure consisting of two united ovules fused basally with the tissues of the receptacle. Pollen tube penetration of the placenta at its tip, development of the zygote at the distal pole, and early endosperm formation at the basal pole of the former megagametophyte indicate that the ovule is orthotropous. A theoretical interpretation of gynoecial phylogeny in Arceuthobium is discussed.  相似文献   
120.
A new cyanogenic glycoside isolated from pods of Acacia sieberiana var. woodii has been shown by chemical and spectroscopic methods to be (2S)-2-[(6-O-α-l-arabinopyranosyl-β-d-glucopyranosyl)oxy]-3-methylbut-3-enenitrileo. Acid-catalysed hydrolysis of the glycoside afforded arabinose and proacacipetalin, and base-catalysed double-bond migration gave 2- [(6-O-α-l-arabinopyranosyl-β- d-glucopyranosyl)oxy ]-3-methylbut-2-enenitrile.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号