全文获取类型
收费全文 | 23349篇 |
免费 | 2212篇 |
国内免费 | 1221篇 |
出版年
2024年 | 56篇 |
2023年 | 578篇 |
2022年 | 777篇 |
2021年 | 1139篇 |
2020年 | 978篇 |
2019年 | 1200篇 |
2018年 | 1049篇 |
2017年 | 831篇 |
2016年 | 936篇 |
2015年 | 1109篇 |
2014年 | 1456篇 |
2013年 | 1884篇 |
2012年 | 1113篇 |
2011年 | 1231篇 |
2010年 | 913篇 |
2009年 | 1092篇 |
2008年 | 1094篇 |
2007年 | 1042篇 |
2006年 | 965篇 |
2005年 | 893篇 |
2004年 | 815篇 |
2003年 | 611篇 |
2002年 | 586篇 |
2001年 | 493篇 |
2000年 | 394篇 |
1999年 | 374篇 |
1998年 | 365篇 |
1997年 | 317篇 |
1996年 | 269篇 |
1995年 | 222篇 |
1994年 | 265篇 |
1993年 | 227篇 |
1992年 | 207篇 |
1991年 | 159篇 |
1990年 | 174篇 |
1989年 | 117篇 |
1988年 | 128篇 |
1987年 | 85篇 |
1986年 | 93篇 |
1985年 | 92篇 |
1984年 | 77篇 |
1983年 | 57篇 |
1982年 | 65篇 |
1981年 | 52篇 |
1980年 | 31篇 |
1979年 | 40篇 |
1978年 | 27篇 |
1976年 | 21篇 |
1975年 | 19篇 |
1974年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 718 毫秒
31.
32.
Sequences related to the major subunit gene fedA of F107 fimbriae in porcine Escherichia coli strains that express adhesive fimbriae 总被引:1,自引:0,他引:1
Abstract Porcine Escherichia coli strains isolated from cases fo postweaning diarrhea or edema disease were analysed for the presence of fedA , the major subunit gene of F107 fimbriae. The E. coli isolates were known to contain colonisation factor '8813', or to express F107, 2134P or other fimbriae, different from F4, F5, F6, and F41. PCR with fedA -specific primers, restriction enzyme digestion of the PCR product, and nucleotide sequence analysis demonstrated that 2134P pili, colonisation factor '8813' and fimbriae identified on Australian strains of the O141 serotype belong to one family of F107 fimbrial antigens. 相似文献
33.
34.
The effects of body size on mating and reproduction in Brachinus lateralis (Coleoptera: Carabidae) 总被引:1,自引:0,他引:1
STEVEN A. JULIANO 《Ecological Entomology》1985,10(3):271-280
Abstract. 1. The causes and reproductive consequences of body size variation of Brachinus lateralis Dejean, a parasitic carabid beetle, were investigated.
2. Body size variation occurs within and between sites. Host size has a major influence on body size of the adult.
3. Fecundity is positively correlated with body size. Egg size is not correlated with body size.
4. Mating males tend to be larger than non-mating males. There is a positive correlation of body sizes in mating pairs.
5. Limited opportunity for host choice may maintain size variation despite the advantages of large size.
6. The non-random patterns of mating for a species without obvious intrasexual aggression suggest that subtle means of male-male competition or female choice may be important. 相似文献
2. Body size variation occurs within and between sites. Host size has a major influence on body size of the adult.
3. Fecundity is positively correlated with body size. Egg size is not correlated with body size.
4. Mating males tend to be larger than non-mating males. There is a positive correlation of body sizes in mating pairs.
5. Limited opportunity for host choice may maintain size variation despite the advantages of large size.
6. The non-random patterns of mating for a species without obvious intrasexual aggression suggest that subtle means of male-male competition or female choice may be important. 相似文献
35.
36.
37.
The uptake of two different preparations of99mTechnetium-methylene diphosphonate in fetal rat calvaria is compared. The localization of99mTc after administration of99mTc(Sn)-MDP and99mTc-MDP showed equal distribution in autoradiography. 相似文献
38.
The groundbreaking technologies of induced pluripotency and lineage conversion have generated a genuine opportunity to address fundamental aspects of the diseases that affect the nervous system. These approaches have granted us unrestricted access to the brain and spinal cord of patients and have allowed for the study of disease in the context of human cells, expressing physiological levels of proteins and under each patient's unique genetic constellation. Along with this unprecedented opportunity have come significant challenges, particularly in relation to patient variability, experimental design and data interpretation. Nevertheless, significant progress has been achieved over the past few years both in our ability to create the various neural subtypes that comprise the nervous system and in our efforts to develop cellular models of disease that recapitulate clinical findings identified in patients. In this Review, we present tables listing the various human neural cell types that can be generated and the neurological disease modeling studies that have been reported, describe the current state of the field, highlight important breakthroughs and discuss the next steps and future challenges. 相似文献
39.
A nationwide health card recording system for dairy cattle was introduced in Norway in 1975 (the Norwegian Cattle Health Services). The data base holds information on mastitis occurrences on an individual cow basis. A reduction in mastitis frequency across the population is desired, and for this purpose risk factors are investigated. In this paper a Bayesian proportional hazards model is used for modelling the time to first veterinary treatment of clinical mastitis, including both genetic and environmental covariates. Sire effects were modelled as shared random components, and veterinary district was included as an environmental effect with prior spatial smoothing. A non-informative smoothing prior was assumed for the baseline hazard, and Markov chain Monte Carlo methods (MCMC) were used for inference. We propose a new measure of quality for sires, in terms of their posterior probability of being among the, say 10% best sires. The probability is an easily interpretable measure that can be directly used to rank sires. Estimating these complex probabilities is straightforward in an MCMC setting. The results indicate considerable differences between sires with regards to their daughters disease resistance. A regional effect was also discovered with the lowest risk of disease in the south-eastern parts of Norway. 相似文献
40.
R.J. Dobson A.P. Dargantes R.T. Mercado 《International journal for parasitology》2009,39(10):1115-1123
Simple demographic and infectious disease models of buffaloes and other domestic hosts for animal trypanosomosis (surra) caused by Trypanosoma evansi were developed. The animal models contained deterministic and stochastic elements and were linked to simulate the benefit of control regimes for surra in village domestic animal populations in Mindanao, Philippines. The impact of the disease on host fertility and mortality were key factors in determining the economic losses and net-benefit from the control regimes. If using a high (99%) efficacy drug in surra-moderate to high risk areas, then treating all animals twice each year yielded low prevalence in 2 years; targeted treatment of clinically sick animals, constantly monitored (monthly), required 75% fewer treatments but took longer to reach a low prevalence than treating all animals twice each year. At high drug efficacy both of these treatment strategies increased the benefit over untreated animals by 81%. If drug efficacy declined then the benefit obtained from twice yearly treatment of all animals declined rapidly compared with regular monitoring and targeting treatment to clinically sick animals. The current control regimen applied in the Philippines of annual sero-testing for surra and only treating sero-positive animals provided the lowest net-benefit of all the control options simulated and would not be regarded as effective control. The total net-benefit from effective surra control for a typical village in a moderate/high risk area was 7.9 million pesos per annum (US $158,000). The value added to buffaloes, cattle, horses, goats/sheep and pigs as a result of this control was US $88, $84, $151, $7, $114 per animal/year, respectively. 相似文献