全文获取类型
收费全文 | 9132篇 |
免费 | 428篇 |
国内免费 | 67篇 |
专业分类
林业 | 1383篇 |
农学 | 233篇 |
基础科学 | 67篇 |
1428篇 | |
综合类 | 761篇 |
农作物 | 275篇 |
水产渔业 | 417篇 |
畜牧兽医 | 4250篇 |
园艺 | 235篇 |
植物保护 | 578篇 |
出版年
2022年 | 80篇 |
2021年 | 111篇 |
2020年 | 146篇 |
2019年 | 85篇 |
2018年 | 244篇 |
2017年 | 211篇 |
2016年 | 248篇 |
2015年 | 207篇 |
2014年 | 191篇 |
2013年 | 460篇 |
2012年 | 422篇 |
2011年 | 400篇 |
2010年 | 260篇 |
2009年 | 191篇 |
2008年 | 343篇 |
2007年 | 405篇 |
2006年 | 362篇 |
2005年 | 301篇 |
2004年 | 271篇 |
2003年 | 258篇 |
2002年 | 231篇 |
2001年 | 167篇 |
2000年 | 172篇 |
1999年 | 140篇 |
1992年 | 122篇 |
1991年 | 128篇 |
1990年 | 154篇 |
1989年 | 160篇 |
1988年 | 139篇 |
1987年 | 131篇 |
1986年 | 129篇 |
1985年 | 119篇 |
1984年 | 115篇 |
1983年 | 93篇 |
1982年 | 64篇 |
1981年 | 58篇 |
1979年 | 128篇 |
1978年 | 93篇 |
1977年 | 96篇 |
1976年 | 63篇 |
1975年 | 79篇 |
1974年 | 114篇 |
1973年 | 117篇 |
1972年 | 95篇 |
1971年 | 111篇 |
1970年 | 78篇 |
1969年 | 91篇 |
1968年 | 71篇 |
1967年 | 68篇 |
1965年 | 59篇 |
排序方式: 共有9627条查询结果,搜索用时 0 毫秒
11.
With the help of a new synthetic material follicles and corpora lutea from the ovaries of 80 cows in different stages of the sexual cycle were examined for modifications of their blood vessel architecture. In the theca externa the main artery which runs towards the follicle, separates into arterioles of which capillaries derive in the theca interna, building a basket-like network around the zona granulosa. After ovulation the follicle wall forms characteristic fields. Capillaries grow into the zona granulosa and thus the folds form the lobular structure of the corpus luteum. Capillaries which rise from the ruptured part of the follicle, spread centripetally and together with lutein cells they build up the not lobulated cupola of the corpus luteum. The regression of the corpus luteum starts around the 16th day of the cycle, beginning at the capillary network of the cupola. A contraction of the vessels and a quick decrease of the volume follow. 相似文献
12.
The anatomical-pathological findings of 15 woolly monkeys were comparable with those described in man with essential benign or malignant hypertension. Kidneys revealed arterio- and arteriolosclerosis or an onion peel-like proliferation, in some cases necrotizing endarteritis. Obesity due to restricted physical activity, unnatural feeding, and psychical and physical stress could have contributed to the development of this condition. Further, high vulnerability of the genus woolly monkey is postulated. Thus, essential hypertension of woolly monkeys appears to be a multifactorial disease. 相似文献
13.
M Steinhardt S Reimer J Kutschke U Bünger 《Archiv fuer experimentelle veterinaermedizin》1989,43(1):111-119
4 female and 2 male untrained fattening pigs, weighing 43.9 +/- 1.6 kg at the beginning of the experiment underwent continuous measurement of VO2, VCO2, and rectal temperature, prior to, during, and after running on a horizontal exercise belt set to speeds of 0.7, 1.3, and 2.5 m.s-1. The highest values of VO2 and VCO2 (ml-min-1/kg-1) and rectal temperature (degrees C) were usually measured few minutes after running. They were 18.84 +/- 3.65 and 20.4 +/- 4.53 as well as 41.2 +/- 0.4, 28.41 +/- 4.07 and 33.26 +/- 5.92 or 41.3 +/- 0.5, 26.21 +/- 7.7 and 32.32 +/- 7.14 as well as 40.5 +/- 0.7, depending on the above belt speeds. Exercise belt speeds of 1.3 to 1.8 m.s-1 were found to be suitable for testing aerobic metabolic capacity of untrained young pigs. 相似文献
14.
The fertility of male coypu sperm following seminal vesicle extirpation was investigated using the penetration test into the egg of Syrian golden hamster (Mesocricetus auratus). Ejaculates were obtained from five males by means of electro-ejaculation under halothane narcosis. The results of the zona-free hamster eggs (ZFHE) penetration test showed that the ejaculates of all the surgically treated coypu males were fertile and that ZFHE value fluctuated from 54 to 76.6%. The results obtained in experiments with natural mating revealed that the extirpation of male coypu seminal vesicles did not affect their fertility. In total 47 foetuses were found post mortem in ten coypu females covered by surgically treated males, which on average represented 4.7 foetuses per female. 相似文献
15.
Bull sperm pellets experimentally infected with various concentrations of Mycoplasma (M.) bovis, M. bovigenitalium, and M. californicum were stored several months at -196 degrees C and were subsequently tested for mycoplasmas, using different methods and culturing media. M. bovis was reliably identified by laboratory diagnosis up to a concentration of 10(2) cfu/pellet. M. bovigenitalium and M. californicum were found to make higher demands on the quality of culturing substrates. Recommended are 1-h broth incubation and 5-d broth breeding. 相似文献
16.
17.
The administration of 20 mg/kg of acetylsalicylic acid in 18 clinically healthy dogs resulted in a thrombocytopathy with lengthened capillary bleeding time and irreversible aggregation inhibition. Through the set up of individual dilution series, one could conclude the proportional percentage of aggregation functional transfused thrombocytes. The capillary bleeding time was shortened after the intravenous injection of prednisolone (5 mg/kg) without measurable influence on the thrombocytes. Compared to the singular use of cortisone or blood transfusion alone, the effect on capillary bleeding time became magnified when one combined transfusion and corticosteroids. The fresh blood conserves (12 hours) were, with respect to the haemostyptical properties, superior to blood stored for 5 days. The component of aggregation-functional thrombocytes was, due to the prophylactic cortisone application prior to transfusion, not increased. 相似文献
18.
There is only limited information on sheep interferon available. Recent publications have reported on: 1. an interferon (IFN) alpha subtype, which is secreted by the fetal trophectoderm into the lumen of the uterus between the 10th and 21st day of gestation. It was therefore named ovine trophoblast protein (oTP-1), and is responsible for signalling pregnancy to the ewe via high affinity receptors in the endometrium. It is thought that oTP-1 acts by directly influencing prostaglandin metabolism. 2. the role of lentivirus-induced interferon (LV-IFN) in the pathogenesis of Maedi/Visna. The results indicate that LV-IFN limits viral replication and therefore contributes to virus persistence and is also responsible for a chronic inflammatory process. 3. the mitogen- or antigen-dependent induction of ovine interferon gamma (IFN gamma) and its characterization. 相似文献
19.
P. Laffaille A. Acou J. Guillouët B. Mounaix A. Legault 《Ecology of Freshwater Fish》2006,15(4):583-588
Abstract – Changes in the numbers and size-class structure of European silver eels, Anguilla anguilla , in the River Frémur (France) were examined over a 9-year period after installation of downstream eel passes. The number of silver eels migrating downstream peaked in 1999, then decreased strongly and steadily after 2000, reaching relatively low levels. At the same time, a gradual shift in the silver eel sex ratio from a dominance of males (size from 270 to 442 mm, age from 3 to 6 years) to females (size from 366 to 1112 mm, age from 4 to 9 years) was recorded. Possible explanations for the escapement patterns observed are environmental sex determination and the installation of eel passes on the main hydraulic engineering structures in 1992 and 1996. 相似文献
20.
In faeces and ileal digesta samples of 31 intact (INT) as well as 73 surgically differently prepared pigs bacterial fractionations and 2.6-diaminopimelic acid (DAP) estimations were carried out in order to calculate the bacterial N proportion in faeces N and digesta N after feeding various diets. Because of a high individual variability and the analytical variation width of the DAP/N-ratios no distinct influences of the fed diets could be found. The average DAP/N-values in the faeces (0.224) of INT pigs ranged in the same magnitude as in the digesta (0.0272) of ileorectostomized (IRA) pigs with open colon descendens (IRAo), where a digesta backflow is possible. Distinct lower DAP/N-ratios (0.0125 resp. 0.0043), however, were found in the digesta of pigs with ileo-caecal cannulae (IZB) or IRA pigs with closed colon (IRAg). On the base of various premises (N of the "bacterial fraction" C is only bacterial N; the DAP found in fraction A originates from intestinal bacteria adhering to feed particles) conducted calculations of the bacterial N proportions (in per cent of total N) led to the following data: Faeces of INT pigs: 43.0 ... 68.2 vs. 69.6 ... 89.0; digesta of operated pigs (except protein free diet) IRAo: 22.3 ... 57.0 vs. 46.2 ... 73.8; IZB: 17.0 ... 35.7 vs. 25.2 ... 53.6; IRAg (only 3 pigs): 23.6 vs. 24.2. The proportion of bacterial N in the digesta N of protein free fed IRAo pigs was 22.0 vs. 22.6%. 相似文献