全文获取类型
收费全文 | 168529篇 |
免费 | 9256篇 |
国内免费 | 100篇 |
专业分类
林业 | 7571篇 |
农学 | 5588篇 |
基础科学 | 1000篇 |
21142篇 | |
综合类 | 26787篇 |
农作物 | 6370篇 |
水产渔业 | 8447篇 |
畜牧兽医 | 87904篇 |
园艺 | 2159篇 |
植物保护 | 10917篇 |
出版年
2019年 | 1653篇 |
2018年 | 2580篇 |
2017年 | 2867篇 |
2016年 | 2647篇 |
2015年 | 2325篇 |
2014年 | 2854篇 |
2013年 | 6775篇 |
2012年 | 5120篇 |
2011年 | 6035篇 |
2010年 | 4087篇 |
2009年 | 4177篇 |
2008年 | 6035篇 |
2007年 | 5828篇 |
2006年 | 5514篇 |
2005年 | 5088篇 |
2004年 | 4868篇 |
2003年 | 4905篇 |
2002年 | 4544篇 |
2001年 | 5615篇 |
2000年 | 5434篇 |
1999年 | 4395篇 |
1998年 | 1748篇 |
1997年 | 1744篇 |
1996年 | 1627篇 |
1995年 | 1928篇 |
1994年 | 1636篇 |
1993年 | 1670篇 |
1992年 | 3337篇 |
1991年 | 3452篇 |
1990年 | 3430篇 |
1989年 | 3487篇 |
1988年 | 3156篇 |
1987年 | 3176篇 |
1986年 | 3145篇 |
1985年 | 2982篇 |
1984年 | 2447篇 |
1983年 | 2177篇 |
1982年 | 1478篇 |
1979年 | 2107篇 |
1978年 | 1692篇 |
1977年 | 1489篇 |
1976年 | 1450篇 |
1975年 | 1524篇 |
1974年 | 1880篇 |
1973年 | 1887篇 |
1972年 | 1880篇 |
1971年 | 1701篇 |
1970年 | 1712篇 |
1969年 | 1604篇 |
1967年 | 1402篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
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
82.
A 3‐year‐old Burmese cat was presented with a history of nonresolving crusted and papular lesions of the face and prior treatment with prednisolone. Skin biopsies revealed typical pox lesions with hyperplasia and ulceration of the epidermis and eosinophilic cytoplasmic inclusion bodies in the epidermal cells. In the upper dermis there was prominent diffuse mast cell infiltration and mild neutrophilic and eosinophilic inflammation. Rare cytoplasmic inclusion bodies were also present in swollen endothelial cells of dermal venules, which showed no other degenerative changes. Histological diagnosis was confirmed by electron microscopic evidence of pox virus particles in inclusion bodies of epidermal cells. The lesions resolved within 6 weeks with systemic antibiotic therapy and supportive care. A 2‐year‐old domestic short‐haired cat was presented with multiple disseminated papular and ulcerative pox lesions with central eschar over the entire body. Histologically, large epidermal inclusion bodies (up to 6 μm in diameter) were present. Widespread haemorrhage and vascular wall necrosis was visible in the dermis and subcutis. Some subcutaneous vessels showed neutrophilic vasculitis. In addition to diffuse dermal neutrophilic and eosinophilic inflammation, a lymphohistiocytic panniculitis was also present. The cat died as a result of massive haemorrhage and lymphedema, despite supportive care. Funding: Self‐funded. 相似文献
83.
A Ogasa T Tsutsui E Kawakami M Sone T Kawarasaki S Iwamura 《The Journal of veterinary medical science / the Japanese Society of Veterinary Science》1991,53(2):181-184
Clinical and endocrinological responses to administration of gonadotropin releasing hormone analog (LH-RH-A) during the lactation period and postweaning in the sow were investigated. Plasma LH concentrations in lactating sows rose immediately after administration of LH-RH-A. However, in postweaning sows the increase of LH level was more slowly. Three of 5 postweaning sows came into estrus and ovulated after LH-RH-A treatment. One sow exhibited a distinct LH response, but her ovaries remained quiescent. The remaining one with feeble estrus for a short period became cystic ovaries. Thus, LH response to GnRH in the sow seems to be higher during early lactation than at 2 days postweaning. 相似文献
84.
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
85.
T Obi A Miyamoto M Matumoto S Ishiguro A Nishio 《The Journal of veterinary medical science / the Japanese Society of Veterinary Science》1991,53(5):789-795
The mechanisms of histamine-induced contraction and relaxation were investigated in rings isolated from a middle part of the left descending coronary arteries of horses. Intact and endothelium-denuded preparations were compared. Rings of horse coronary arteries contracted in response to histamine in a concentration dependent manner, but some of them relaxed with lower concentrations and contracted with higher concentrations. Removal of the endothelium abolished the relaxation and potentiated the contraction. The pD2 values were 4.70 +/- 0.08 in the rings with intact endothelium and 4.95 +/- 0.08 in endothelium-denuded rings. Histamine-induced contractions in intact and denuded preparations were not affected by an H2-antagonist, cimetidine, but were inhibited by an H1-antagonist, diphenhydramine in non-competitive manner in the rings with endothelium and in competitive manner in denuded rings. After precontraction with PGF2 alpha or norepinephrine, histamine relaxed preparations with intact endothelium (pD2 value, 7.80 +/- 0.11), although histamine-induced relaxations were not observed in denuded preparations. The relaxation was competitively inhibited by diphenhydramine. Relaxing response was significantly attenuated by methylene blue, quinacrine, L-nitro-arginine, gossypol and AA861 but not by indomethacin. These results suggest that the histamine-induced contraction and relaxation in horse coronary arteries are mediated mainly by H1-receptors in the smooth muscle and endothelium, respectively, and H1-receptor activation of endothelial cells may liberate vasodilator substances. 相似文献
86.
C M Honnas 《Veterinary Clinics of North America: Equine Practice》1991,7(3):695-722
Several surgical conditions affecting the foot can be successfully managed with the horse standing. Many factors affect the clinician's choice of whether to perform surgery with the horse standing or anesthetized. Temperament or pregnancy of the horse and economics may influence the decision to perform surgery with the horse standing. This article discusses several foot conditions that can be treated successfully in the ambulatory horse. 相似文献
87.
88.
H Amasaki S Matsumoto M Takanosu M Daigo 《The Journal of veterinary medical science / the Japanese Society of Veterinary Science》1991,53(6):1031-1036
The present study describes histological alterations and immunohistochemical distributions of extracellular matrices (ECMs) and the carbonic anhydrase isozyme-III (CA-III) during the period of bovine palatine ridge formation. Morphogenesis of bovine palatine ridges was preceded by epidermal placodes and the mesenchymal condensation (MC). During the early stages of less than 44 cm crown rump length (CRL), fibronectin (FN) was distributed densely in the MC. Strong reactions against type I collagen (C-1) were detected outer to the FN positive site. In the stages of more than 44 cm CRL, FN and C-1 were distributed diffusely in subepithelial mesenchyme. Laminin (LN) and type IV collagen were distributed in the epithelial and endothelial basement membranes (BMs) in all of the stages examined, except in the stage of 7 cm CRL, where LN was not detected only in the BM just beneath the epidermal placode. CA-III was detected in basal epithelial cells except for palatine ridge rudiments in the stages of more than 21 cm CRL. It is suggested that the expressions of LN and CA-III might play a role in the spatial determination of rudiments of bovine fetal palatine ridges. 相似文献
89.
T M Frye S N Williams T W Graham 《Veterinary Clinics of North America: Food Animal Practice》1991,7(1):217-275
Deficiencies of vitamins A, D, K, E and thiamin can cause severe limitations in beef production. In particular, vitamin A and E can be common causes of lost profit, secondary to limitations of reproductive and growth potential. Prolonged dry periods will reduce available A and E in pasture forage, as can ensiling and prolonged storage of harvested feedstuffs. Polioencephalomalacia is a thiamin responsive disorder, associated with high concentrate feeding and lush pastures. Antimetabolites, such as amprolium, will cause thiamine deficiency when fed in excess. Recent information has shown improved performance with supplemental beta carotene and niacin. The positive responses in reproductive performance, noted with cattle fed supplemental beta carotene, was independent of vitamin A. Supplementation of vitamins above National Research Council recommendations can be justified. However, proper evaluation of feed and animal status, and documentation of a response to supplementation is necessary before diagnosing deficiencies of specific nutrients. 相似文献
90.
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