全文获取类型
收费全文 | 92943篇 |
免费 | 5695篇 |
国内免费 | 771篇 |
专业分类
林业 | 4106篇 |
农学 | 2901篇 |
基础科学 | 749篇 |
12233篇 | |
综合类 | 16750篇 |
农作物 | 3485篇 |
水产渔业 | 4833篇 |
畜牧兽医 | 47021篇 |
园艺 | 1335篇 |
植物保护 | 5996篇 |
出版年
2021年 | 981篇 |
2020年 | 1036篇 |
2019年 | 1200篇 |
2018年 | 1816篇 |
2017年 | 2024篇 |
2016年 | 1835篇 |
2015年 | 1676篇 |
2014年 | 1927篇 |
2013年 | 3529篇 |
2012年 | 3587篇 |
2011年 | 4141篇 |
2010年 | 2675篇 |
2009年 | 2575篇 |
2008年 | 3625篇 |
2007年 | 3464篇 |
2006年 | 3067篇 |
2005年 | 3004篇 |
2004年 | 2658篇 |
2003年 | 2686篇 |
2002年 | 2487篇 |
2001年 | 2711篇 |
2000年 | 2747篇 |
1999年 | 2121篇 |
1998年 | 843篇 |
1997年 | 746篇 |
1996年 | 695篇 |
1995年 | 782篇 |
1992年 | 1636篇 |
1991年 | 1815篇 |
1990年 | 1737篇 |
1989年 | 1702篇 |
1988年 | 1571篇 |
1987年 | 1633篇 |
1986年 | 1664篇 |
1985年 | 1488篇 |
1984年 | 1251篇 |
1983年 | 1077篇 |
1982年 | 716篇 |
1979年 | 1145篇 |
1978年 | 907篇 |
1977年 | 749篇 |
1976年 | 759篇 |
1975年 | 788篇 |
1974年 | 1088篇 |
1973年 | 1048篇 |
1972年 | 1033篇 |
1971年 | 961篇 |
1970年 | 881篇 |
1969年 | 836篇 |
1967年 | 725篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Calcium fluxes were measured, in vivo, in both directions across the ovine reticulorumen wall of four sheep when the luminal potassium concentration was either 30 mmol litre-1 or 90 mmol litre-1. Neither fluxes were affected by an increased potassium concentration although net magnesium absorption was decreased (PO less than 0.05) and the transmural potential difference was increased (P less than 0.01) under these conditions. The results obtained suggest that, unlike magnesium, calcium is transported bidirectionally across ovine ruminal tissue independently of the transmural potential difference across the rumen wall. 相似文献
52.
CERES-Maize (Vl. 0) predicted no grain yield when 100% defoliation occurred during vegetative growth. This result conflicted with field observations where 100% defoliation early in the vegetative stage did not materially reduce grain yield. CERES-Maize was modified to realistically predict yields when defoliation greater than 50% occurred during vegetative growth by taking into account stem (stem proper and sheath) photosynthesis and translocation of dry matter from the stem to the developing leaves. With these modifications, predictions from CERES-Maize were in good agreement with field measurements when defoliation occurred both early and later in the vegetative stage. This modified version of CERES-Maize can be the basis of a decision support system for defoliating pests of corn where yields can be evaluated under different management strategies and climate scenarios. 相似文献
53.
L.E. Young D.H. Bartram M. Diamond A. Gregg R.S. Jones 《Veterinary anaesthesia and analgesia》1991,18(Z1):171-174
54.
L A Janssens 《Veterinary surgery : VS》1991,20(4):274-278
Seven foci of pain (trigger points) were identified in the triceps brachii, infraspinatus, adductor-pectineus, peroneus longus, gluteus medius, ileocostorum lumborum, and quadriceps femoris muscles in 48 lame dogs. The dogs had been lame for 1 day to 150 weeks (mean, 24 weeks). Thirty-one dogs had been treated unsuccessfully with corticosteroids, nonsteroidal anti-inflammatory drugs, analgesics, or acupuncture. Palpating the trigger points induced severe pain. Treatment consisted of weekly stimulation of the trigger points by needling or injection of a local anesthetic. The mean treatment period was 2.8 weeks. Excellent results and complete recovery were observed in 34 dogs (60%). 相似文献
55.
R. Iori O. Leoni L. Lazzeri G. Mosca S. Palmieri 《Journal of Agronomy and Crop Science》1991,167(2):91-95
Samples of rapeseed from three Italian growing environments (Bologna, Perugia and Palermo) were analysed for glucose content and dry weight of 1000 seeds every three or four days starting from the end of flowering until complete ripening. In addition, the content of oil, soluble and total proteins, glucosinolates and myrosinase activity was determined in samples of mature seeds. The cultivars used were jet Neuf and Lingot (type 0) and Tandem, Jade and Santana (type 00). From the results it emerged that the point of intersection of the two branches of the linear regression plots for different glucose-consumption kinetics found during seed filling, in addition to being strongly affected by the climate of the test environment, is correlated with quantitative and qualitative production, independently of the genotype. 相似文献
56.
J Sherrill T Schock J L Dunn D J St Aubin V V Burnley S E Poet 《Journal of zoo and wildlife medicine》2001,32(1):17-24
Humoral immune responses of black-footed penguins (Spheniscus demersus) to DNA-mediated immunization with a beta-galactosidase reporter gene expression plasmid were evaluated. Six male and 6 female adult penguins received either test plasmid, pCMV-beta, containing the beta-galactosidase gene or control plasmid, pCI, lacking a gene for expression. Three birds from each group were used previously in a diluent control group and given one injection of sterile saline. All samples were screened for anti-beta-galactosidase antibodies by indirect enzyme-linked immunosorbent assay with anti-chicken immunoglobulin G as secondary antibody. Antibodies to beta-galactosidase were detected in the sera of pCMV-beta-inoculated penguins, with a peak response on day 21. Antibody titers of the test plasmid group versus both control groups on days 21, 28, and 42 differed significantly. These results demonstrate that black-footed penguins can be safely transfected with the gene encoding beta-galactosidase and will mount a humoral response against the in vivo-expressed protein. Knowledge from this initial study can be applied to the development of DNA-mediated vaccines against specific infectious diseases of penguins. 相似文献
57.
The utilization of dietary lysine for protein synthesis is affected by the digestibility of protein-bound lysine, by its intestinal resorption and by its oxidative catabolism. The approach chosen in this paper enables a comparison of the cumulative effect of these processes on the utilization of free and protein-bound lysine, respectively. The principle of the approach is based on a quantification of the expiration of 14C-labelled carbon dioxide after an oral administration of a diet, which contains L-(U-14C)-lysine either as a free amino acid or bound to yeast proteins. During an adaptation phase cockerels of the Japanese quail received a diet based mainly on ground wheat and wheat gluten. This diet was supplemented either with yeast proteins or with a mixture of L-amino acids which simulates the composition of the yeast proteins. In the main experiment the expiration of labelled carbon dioxide was measured during 240 minutes after the administration of the corresponding labelled diets. Just before treatment the animals were either in the postprandial phase or in a state of slight hunger. The maximum of expiration of labelled carbon dioxide occurred around the 60th minute after administration of the corresponding labelled diets. The cumulative expiration of labelled carbon dioxide, expressed in per cent of the radioactive dose used, amounts to 15.5% and 14.3% for free and protein-bound lysine, respectively. The utilization of both forms of lysine in the Japanese quail is lower than in broilers. 相似文献
58.
59.
A porcine in vitro fertilization (IVF) system and seminal quality parameters of frozen–thawed boar semen were used to assess the effectiveness of two different thawing rates of frozen boar semen, and to address the question of whether differences between fertility of ejaculates could be predicted in a limited field trial. In the first experiment, two thawing procedures were analysed (37°C, 30 s; 50°C, 12 s) and no differences in sperm quality were found. However, when the procedure was 50°C, 12 s the IVF results showed a higher number of sperm per penetrated oocyte and a near 10 points higher rate of pronuclear formation. In the second experiment, the fertility results obtained in the limited field trial show to be efficient enough for application in a commercial use, especially for three of the employed boars (fertility ≥80%). In this limited study, the conventional seminal parameters are not accurate enough to discriminate good and bad boars in relation to fertility. On the contrary, parameters of in vitro penetrability are more precise to predict subsequent fertilities. As conclusion, the IVF fertilization system seems to be a good tool to evaluate the quality of frozen–thawed boar semen previous to its commercial way, to verify the bank semen storage quality and a good way to assay new sperm freezing procedures, as it is the more precise evaluating method in estimating the potential fertilizing ability. 相似文献
60.
Jennifer L Davis 《Veterinary Clinics of North America: Equine Practice》2003,19(3):765-778
In summary, peritonitis in the horse is a potentially life-threatening disease that must be treated promptly and aggressively. Therapy should be aimed at reducing systemic shock and hypovolemia, correction of the primary cause, antibiotic and anti-inflammatory therapy, and abdominal drainage and lavage. The prognosis depends on the ability to diagnose and treat the underlying cause and prevent the development of complications. Mortality rates can be as high as 59.7%, with horses developing postoperative peritonitis having a 56% mortality rate. Long-term complications like adhesion formation or internal abscesses may further reduce the survival rate. The prognosis is best determined by an early and quick response to aggressive treatment. 相似文献