全文获取类型
收费全文 | 4127篇 |
免费 | 275篇 |
国内免费 | 2篇 |
出版年
2023年 | 20篇 |
2022年 | 56篇 |
2021年 | 103篇 |
2020年 | 59篇 |
2019年 | 73篇 |
2018年 | 101篇 |
2017年 | 96篇 |
2016年 | 139篇 |
2015年 | 223篇 |
2014年 | 200篇 |
2013年 | 286篇 |
2012年 | 341篇 |
2011年 | 367篇 |
2010年 | 221篇 |
2009年 | 181篇 |
2008年 | 255篇 |
2007年 | 244篇 |
2006年 | 209篇 |
2005年 | 208篇 |
2004年 | 178篇 |
2003年 | 171篇 |
2002年 | 150篇 |
2001年 | 42篇 |
2000年 | 32篇 |
1999年 | 24篇 |
1998年 | 34篇 |
1997年 | 31篇 |
1996年 | 23篇 |
1995年 | 25篇 |
1994年 | 19篇 |
1993年 | 30篇 |
1992年 | 16篇 |
1991年 | 10篇 |
1990年 | 16篇 |
1989年 | 16篇 |
1988年 | 9篇 |
1987年 | 11篇 |
1986年 | 12篇 |
1985年 | 12篇 |
1984年 | 17篇 |
1983年 | 11篇 |
1982年 | 17篇 |
1981年 | 6篇 |
1980年 | 12篇 |
1979年 | 9篇 |
1977年 | 7篇 |
1976年 | 7篇 |
1975年 | 8篇 |
1974年 | 19篇 |
1966年 | 5篇 |
排序方式: 共有4404条查询结果,搜索用时 109 毫秒
11.
Data obtained from follow up of the 1971 census sample in the Office of Population Censuses and Surveys longitudinal study of England and Wales were used to look at women''s mortality differentials at ages 15-59. Women were grouped by combining information on marital state, own occupation, husband''s occupation (if married), economic activity, and indicators of household wealth (housing tenure and access to a car). Large groups were found with considerable differences in mortality. High mortality was associated with working in manual occupations and living in rented housing with no car in the household. In contrast, low mortality was associated with non-manual occupations and living in owner occupied housing with a car. Among married housewives and single women these extreme groups contributed 44% of expected deaths, the disadvantaged group experiencing death rates two and a half times that of the advantaged group. Smaller differences were found among married women with an occupational class.These findings are further evidence of the “health divide” in England and Wales and show that accurately to reflect the relation between a woman''s life circumstances and mortality it is necessary to utilise other measures than those based solely on occupation. 相似文献
12.
Determination was made of the proportion of selected by-products (acetaldehyde, ethyl acetate, methanol, propanol, isobutanol, 2-methyl-butanol, 3-methyl-butanol) of batch and continuous ethanol fermentation carried out with the use of yeastSaccharomyces cerevisiae, strain 0–11, cells immobilized by adsorption on selected carriers (foamed polystyrene, bone shot, beech wood chips, porous glass) as well as by entrapping in calcium alginate and calcium pectinate gel. 相似文献
13.
Summary
Tylosema esculentum, a perennial geophyte bearing yellow distylous flowers in racemes, maintains a high degree of outbreeding through reciprocal herkogamy. In addition, a viscous liquid, the anther-mucilage, is produced by the anther connective tissue and released concurrently with the pollen. The polysaccharide- and lipid-rich mucilage, which is functional in the shedding and transfer of pollen, is available for more than 1 day due to the gradual solidification of the mucilage. The assimilation of the pollen with the liquid substance significantly affects the pollination biology of T. esculentum. This is the first report on the unique phenomenon of wet pollen in the Caesalpiniaceae. 相似文献
14.
Annikki Liakka Meeri Apaja-Sarkkinen Tuomo Karttunen Helena Autio-Harmainen 《Cell and tissue research》1991,263(2):245-252
Summary The immunohistochemical distribution of the basement membrane (BM) proteins, laminin and type IV collagen, and interstitial type III collagen was investigated in 12 fetal spleens at the 15th–38th gestational weeks (g.w.) and in spleens of 8 infants from term to 4 years. The results were compared with the distribution of the same proteins in adult human spleen. BM proteins were found to be abundantly present in the red pulp of all spleens during the whole of development. The content of type III collagen gradually decreased with advancing age and, in adult spleen, there were only occasional positively staining fibers in Billroth's cords. This finding indicates that the composition of reticular fibers in the red pulp of spleen is different from the reticular fibers elsewhere in lymphoreticular tissue. Early signs of ring fiber formation in the walls of venous sinuses were detectable at the 15th–19th g.w., although their more complete development occurred relatively late from the 36th g.w. onwards. Ring fibers contained both laminin and type IV collagen in all the investigated spleens. They never stained for type III collagen. The developing white pulp was positive for BM proteins, but showed no staining for type III collagen at the 15th g.w. At later ages, the white pulp stained similarly for both BM proteins and type III collagen. 相似文献
15.
A cDNA probe for the low density lipoprotein (LDL) receptor gene was used to screen DNA samples from 52 unrelated Finnish patients with the heterozygous form of familial hypercholesterolemia (FH) and 51 healthy controls. Southern blot analysis using the restriction enzyme PvuII revealed an abnormal 11 kb (kilo base-pair) restriction fragment in 16 (31%) of the patients but none of the controls. A more detailed restriction enzyme analysis of the DNA from patients revealed a mutation which apparently is due to an 8 kb deletion extending from intron 15 to exon 18 of the LDL receptor gene. Co-segregation of FH with the mutated gene was demonstrated in three families. These data are consistent with a ‘founder gene effect’ and support the assumption that recombinant DNA methods may have great impact on the diagnostics of FH in genetically homogeneous populations. 相似文献
16.
17.
18.
Data are presented on the aboveground and underground biomass of the speciesMarsilea quadrifolia and on the water regime and soil conditions in a habitat of this species in Central Europe (Czechoslovakia). 相似文献
19.
Heikki O. Laurila Helena Nevalainen Veijo Mäkinen 《Applied microbiology and biotechnology》1985,21(3-4):210-212
Summary Protoplast formation in Curvularia inaequalis was achieved using non-commercial and commercial snail gut enzymes or Trichoderma harzianum enzymes. The cells were grown for enzyme treatment on cellophane sheets or in liquid cultures for varying periods of time. The production of T. harzianum enzymes is discussed. The highest protoplast yields were 2.6x107 protoplasts/ml enzyme solution. Protoplasts were shown to have zero to four nuclei. Protoplast regeneration was succesfully carried out in semisolid agar. 相似文献
20.