全文获取类型
收费全文 | 67270篇 |
免费 | 3043篇 |
国内免费 | 46篇 |
专业分类
林业 | 2898篇 |
农学 | 1799篇 |
基础科学 | 458篇 |
7121篇 | |
综合类 | 15480篇 |
农作物 | 2672篇 |
水产渔业 | 2646篇 |
畜牧兽医 | 32727篇 |
园艺 | 804篇 |
植物保护 | 3754篇 |
出版年
2018年 | 644篇 |
2017年 | 660篇 |
2016年 | 650篇 |
2014年 | 656篇 |
2013年 | 2099篇 |
2012年 | 1464篇 |
2011年 | 1771篇 |
2010年 | 1106篇 |
2009年 | 1026篇 |
2008年 | 1686篇 |
2007年 | 1663篇 |
2006年 | 1624篇 |
2005年 | 1630篇 |
2004年 | 1543篇 |
2003年 | 1620篇 |
2002年 | 1572篇 |
2001年 | 1547篇 |
2000年 | 1530篇 |
1999年 | 1278篇 |
1997年 | 582篇 |
1995年 | 631篇 |
1994年 | 607篇 |
1993年 | 604篇 |
1992年 | 1338篇 |
1991年 | 1433篇 |
1990年 | 1484篇 |
1989年 | 1522篇 |
1988年 | 1428篇 |
1987年 | 1389篇 |
1986年 | 1445篇 |
1985年 | 1398篇 |
1984年 | 1182篇 |
1983年 | 1032篇 |
1982年 | 749篇 |
1981年 | 712篇 |
1980年 | 660篇 |
1979年 | 1146篇 |
1978年 | 940篇 |
1977年 | 840篇 |
1976年 | 778篇 |
1975年 | 876篇 |
1974年 | 1136篇 |
1973年 | 1081篇 |
1972年 | 1145篇 |
1971年 | 1089篇 |
1970年 | 1034篇 |
1969年 | 882篇 |
1968年 | 718篇 |
1967年 | 850篇 |
1966年 | 706篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
201.
202.
203.
C P Moore J B Shaner R M Halenda C S Rosenfeld W K Suedmeyer 《Journal of zoo and wildlife medicine》1999,30(3):423-430
A 5-wk-old female dromedary camel (Camelus dromedarius) was clinically diagnosed with bilateral corneal dermoids, incomplete congenital cataracts, a left persistent hyaloid artery (PHA), and a ventricular septal defect (VSD). The corneal dermoids were removed by lamellar keratectomy, and vision improved in the left eye. Thirteen months after dermoid surgery, the calf was presented for enlargement of the right eye. Glaucoma was confirmed in the right eye, and corneal fibrosis and cataract were noted in the left eye. Persistence of the VSD was confirmed by cardiac ultrasonography. The calf was euthanized, and necropsy findings confirmed VSD. Histopathologic examination revealed bilateral corneal thinning and fibrosis, cataracts with retrolental fibroplasia, and retinal dysplasia. Additional changes in the right globe were anterior segment dysgenesis, ruptured lens capsule, chronic phacoclastic uveitis, and retinal separation. The PHA was confirmed in the left eye. 相似文献
204.
The objective of this study was to evaluate the quality of published literature on reproduction in dogs. A systematic search in online databases revealed 287 papers that met the inclusion criteria. For evaluation a questionnaire comprising 40 criteria regarding materials and methodology, study design, statistics, presentation and information content, applicability and conclusions was developed. In a pre‐test including seven independent scientists the applicability and explanatory power of the questionnaire and its results were validated. Out of 287 publications evaluated, 90 (31.4%) were classified as clinical trials. The remaining 197 publications were case reports or contained information based on personal experience. Not a single meta‐analysis was found. Sixty (66.7%) of the 90 clinical trials included a control group. Randomization was conducted in 23 and blinding in eight articles respectively. In total five articles were determined as randomized, controlled and blinded clinical trials. Information content of the publications was variable concerning details on included animals, type or dosage of used remedies or conducted interventions. For example, in 99.7% of the articles, the exact number of animals was given, but in 79.8%, housing and feeding of the animals were not described. Statistical procedures of clinical trials were determined adequate in 55.6%. However, the data of 67.9% of the articles were evaluated to be not sufficient to draw valid conclusions. This study revealed evidence of deficits in the field of canine reproduction. The demand for more high quality clinical research is obvious. Requisite for the further implementation of the evidence‐based veterinary medicine is an improvement of the quantity and the quality of well‐designed, conducted and reported clinical trials. The practitioner should always assess the quality of information before implementing results into practice to provide best available care for the animals. 相似文献
205.
Summary. After the 4- or 5-leaf stage in young barley plants, there is a decrease in the translocation of 2,4-D from the leaves to the root system. It is shown that there is no relation between this phenomenon and ear initiation, which occurs at this stage of development. Movement of 2,4-D out of leaves of the tiller in the axils of the 1st and 2nd leaves was also shown to be very small. There is some evidence for a'block'in the movement of 2,4-D in established grass plants.
La migration du 2,4-D marqué dans l'orge 相似文献
La migration du 2,4-D marqué dans l'orge 相似文献
206.
207.
The eyes of 20 young cattle were examined over an 18 month period in which 12 members of the group contracted infectious bovine keratoconjunctivitis (IBK). On each of 23 occasions cultural, biochemical and immunoreactive properties of up to 6 isolates of Moraxella bovis derived from each eye were determined. Relationships between the clinical response of eyes, phenotypic properties of M. bovis and annual variations in the level of solar ultraviolet radiation of 280 to 320 nm wavelength were examined. M. bovis was isolated from all IBK-affected and some unaffected eyes less than one month after the maximum annual level of the mean weekly UV radiation (2,840 mWh.m-2 X nm-1) was recorded. A high proportion of M. bovis from IBK lesions were simultaneously active in haemolysis, agar corrosion, gelatin liquefaction and litmus milk peptonisation. Some of these characteristics showed marked dissociation despite consistent reactivity in the fluorescent antibody test, which had a sensitivity and specificity of 95%. Fall in the mean weekly level of UV radiation below 1,438 mWh X m-2 X nm-1 in autumn was accompanied by healing of ulcers, persistent scar formation and a decline in the number of M. bovis isolated from affected eyes. A slower decline in the number of M. bovis isolated from apparently healthy eyes occurred in the winter and occasional fresh IBK lesions occurred.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
208.
Cleaving yeast and Escherichia coli genomes at a single site 总被引:13,自引:0,他引:13
The 15-megabase pair Saccharomyces cerevisiae and the 4.7-megabase pair Escherichia coli genomes were completely cleaved at a single predetermined site by means of the Achilles' heel cleavage (AC) procedure. The symmetric lac operator (lacOs) was introduced into the circular Escherichia coli genome and into one of the 16 yeast chromosomes. Intact chromosomes from the resulting strains were prepared in agarose microbeads and methylated with Hha I (5'-GCGC) methyltransferase (M.Hha I) in the presence of lac repressor (LacI). All Hae II sites (5'-[sequence: see text]) with the exception of the one in lacOs, which was protected by LacI, were modified and thus no longer recognized by Hae II. After inactivation of M.Hha I and LacI, Hae II was used to completely cleave the chromosomes specifically at the inserted lacOs. These experiments demonstrate the feasibility of using the AC approach to efficiently extend the specificity of naturally occurring restriction enzymes and create new tools for the mapping and precise molecular dissection of multimegabase genomes. 相似文献
209.
The Australasian and Ivory Coast deep-sea microtektites have fission track ages of 0.71 and 1.09 million years, respectively. These ages are in good agreement with the ages of deposition of the microtektites determined from paleomagnetic data. Both the fission track ages and ages of deposition of the microtektites agree with the potassium/ argon and fission track ages of tektites from the respective tektite strewn fields. 相似文献
210.