全文获取类型
收费全文 | 211711篇 |
免费 | 11172篇 |
国内免费 | 124篇 |
专业分类
林业 | 8544篇 |
农学 | 6420篇 |
基础科学 | 1483篇 |
24355篇 | |
综合类 | 39798篇 |
农作物 | 8119篇 |
水产渔业 | 10146篇 |
畜牧兽医 | 107380篇 |
园艺 | 2603篇 |
植物保护 | 14159篇 |
出版年
2018年 | 2507篇 |
2017年 | 2770篇 |
2016年 | 2637篇 |
2015年 | 2315篇 |
2014年 | 2759篇 |
2013年 | 7950篇 |
2012年 | 5364篇 |
2011年 | 6651篇 |
2010年 | 4294篇 |
2009年 | 4306篇 |
2008年 | 6611篇 |
2007年 | 6182篇 |
2006年 | 5951篇 |
2005年 | 5620篇 |
2004年 | 5568篇 |
2003年 | 5549篇 |
2002年 | 5449篇 |
2001年 | 6535篇 |
2000年 | 6370篇 |
1999年 | 4981篇 |
1998年 | 2115篇 |
1997年 | 2154篇 |
1995年 | 2503篇 |
1994年 | 2331篇 |
1993年 | 2219篇 |
1992年 | 4514篇 |
1991年 | 4807篇 |
1990年 | 4792篇 |
1989年 | 4788篇 |
1988年 | 4385篇 |
1987年 | 4517篇 |
1986年 | 4658篇 |
1985年 | 4464篇 |
1984年 | 3750篇 |
1983年 | 3363篇 |
1982年 | 2312篇 |
1981年 | 2176篇 |
1980年 | 2063篇 |
1979年 | 3371篇 |
1978年 | 2850篇 |
1977年 | 2366篇 |
1976年 | 2213篇 |
1975年 | 2325篇 |
1974年 | 3051篇 |
1973年 | 3130篇 |
1972年 | 3052篇 |
1971年 | 2801篇 |
1970年 | 2635篇 |
1969年 | 2428篇 |
1967年 | 2064篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
121.
The state of mucus synthesis in the goblet cells of the small intestine was studied in conventional piglets infected with a dose of 200,000 oocytes of the coccidium Isospora suis the first and fifth day after parturition. The synthesis of mucus and its chemical characteristics undergo significant changes during the third and fourth day after infection. The activity of acid and neutral mucous substances declines; their level and the physiological synthetic function of goblet cells begin to return to the normal during the period starting on the eight to tenth day after infection. However, there were no fully functioning goblet cells in the broken numerical ratio even at the end of the period of investigation, i.e. the 13th day after infection. The thin surface layer of mucus remained almost unchanged within the whole extent of the small intestine parts studied. 相似文献
122.
123.
This article reviews recent diagnostic procedures that have arisen over the last 10 years. Videoendoscopy of horses on a high-speed treadmill allows observation of some of the changes that take place in a horse's airway during exercise. Measurements of upper airway airflows and transupper airway pressure, the use of an esophageal balloon and a Ventigraph to measure changes in pleural pressure, and pulmonary function testing are new techniques that aid the researcher in understanding the mechanics and pathologic characteristics of airway diseases and help the practitioner in assessing the severity of a problem, measuring response to therapy, and accurately determining a prognosis. 相似文献
124.
125.
Totally 13575 ewes of two different breeds, Dala and Spel, were inseminated with semen, frozen in straws and thawed at 70°C for 8 sec. An insemination dose of 0.2 ml containing approx. 150 × 106 spermatozoa with at least 45 to 50% progressive motility was imerted 5 to 12 mm into the cervix. The insemination was performed once between 12 and 30 h after the onset of heat. The NR rate of the Dala ewes increased significantly during the season. The NR rate of the ewes inseminated before 15. November was 44.3%, from 15. to 20. November 52.2%. from 20. to 25. November 55.3% and from 25. November and later 61.4%. The corresponding values for the ewes of the Spel breed were 57.3, 58.7, 61.5 and 71.0% respectively, and only the difference between the two last values was statistically significant. The difference between the fertility of the two breeds was significant within each of the periods . 相似文献
126.
Individual antigens of goats 总被引:1,自引:0,他引:1
127.
As anaerobic sampling and culture techniques improved, the documented prevalence of anaerobic bacteria in periodontal disease has increased. The anaerobic bacteria have become more well-known in humans and consequently in dogs, since this species is a major model in periodontal studies. A review of the literature related to anaerobic flora is described. 相似文献
128.
RNA was extracted from single or small groups of ovine ovarian follicles after treatment of ewes with FSH and/or LH. The content of mRNA for the alpha-inhibin and beta A-inhibin subunits was analyzed by hybridization with specific cDNA probes. All ewes were treated with progestin vaginal pessaries to suppress spontaneous preovulatory follicle maturation and ewes were given three intramuscular injections of gonadotropins at 8-hr intervals starting 24 hr prior to collection of ovaries. In experiment I, both Schering-FSH and NIDDK-oFSH-17 (oFSH) significantly increased alpha- and beta A-inhibin mRNA per ewe in 2-5 mm follicles and tended to increase alpha- and beta A-inhibin mRNA in large (greater than 5 mm) follicles. In experiment II, oFSH and NIDDK-oLH-25 (oLH) were administered in a 2X2 factorial arrangement. Separate administration of oFSH or oLH increased (P less than .05) the alpha-inhibin mRNA concentration in large follicles. alpha-inhibin mRNA concentration in 4-5 mm follicles was also increased by oFSH but was decreased by oLH. Concomitant treatment with oFSH and oLH did not change alpha-inhibin mRNA concentrations from those measured in oFSH treated ewes. In experiment II, beta A mRNA concentrations followed a pattern similar to that of alpha A mRNA, but the differences were not statistically significant. We conclude that, in the ewe, exogenous FSH increases the concentration of inhibin mRNA in the whole follicle. The ability of exogenous oLH to alter expression of the inhibin subunit genes may depend upon the stage of follicle maturation. 相似文献
129.
Cellular alterations in level of expression of mRNA encoding for prostaglandin endoperoxide synthase were quantified within ovarian tissues of sheep obtained before, during and after induction of the preovulatory surge of LH and ovulation with LHRH. This was accomplished by isotopic in situ hybridization using a selective cRNA probe to ovine prostaglandin endoperoxide synthase mRNA. A significant elevation in mRNA was detected within the theca interna of the preovulatory follicle at 8, 16 and 24 hr following administration of LHRH. Very close to the time of ovulation (ie., at 24 hr post-LHRH) a marked rise in mRNA was observed in association with epithelial cells covering the apical surface of the follicle. Ovarian cyclooxygenase metabolites of arachidonic acid produced during the ovulatory process in the ewe originate within the thecal layer and germinal epithelium of the follicle destined to ovulate. 相似文献
130.
Y Sugawara K Hirasawa M Takeda J S Han K Doi 《The Journal of veterinary medical science / the Japanese Society of Veterinary Science》1991,53(3):463-468
One-month-old Syrian hamsters of the APA and Std: golden strains were inoculated intraperitoneally with 10(5) PFU/head of the D variant of encephalomyocarditis (EMC) virus and examined virologically and pathologically up to 7 days after inoculation. APA hamsters developed apparent hyperglycemia due to pancreatic islet cell damage while Std:golden hamsters did not. Hamsters of both strains showed clear histopathologic changes in the testis with prominent viral replication as well as in the brain, heart and exocrine pancreas. The susceptibility to EMC virus-infection was higher in males than in females and in APA than in Std: golden hamsters. 相似文献