首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   123551篇
  免费   6299篇
  国内免费   86篇
林业   6271篇
农学   4112篇
基础科学   693篇
  14066篇
综合类   20864篇
农作物   4827篇
水产渔业   5997篇
畜牧兽医   64281篇
园艺   1527篇
植物保护   7298篇
  2018年   1617篇
  2017年   1746篇
  2016年   1663篇
  2015年   1475篇
  2014年   1778篇
  2013年   4567篇
  2012年   3132篇
  2011年   3825篇
  2010年   2549篇
  2009年   2404篇
  2008年   3696篇
  2007年   3676篇
  2006年   3439篇
  2005年   3240篇
  2004年   3088篇
  2003年   3098篇
  2002年   2910篇
  2001年   3941篇
  2000年   3869篇
  1999年   3142篇
  1998年   1274篇
  1997年   1223篇
  1995年   1349篇
  1994年   1126篇
  1993年   1152篇
  1992年   2464篇
  1991年   2658篇
  1990年   2833篇
  1989年   2685篇
  1988年   2501篇
  1987年   2453篇
  1986年   2426篇
  1985年   2405篇
  1984年   2004篇
  1983年   1730篇
  1982年   1202篇
  1979年   1883篇
  1978年   1487篇
  1977年   1219篇
  1976年   1241篇
  1975年   1317篇
  1974年   1690篇
  1973年   1726篇
  1972年   1735篇
  1971年   1661篇
  1970年   1574篇
  1969年   1436篇
  1968年   1224篇
  1967年   1307篇
  1966年   1213篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
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   
82.
For practical reasons, a large volume (i.e. 5 ml) of frozen boar semen per insemination dose is desirable, but successful freezing has not been achieved, since optimal cooling rates have not yet been established. Post-thaw motility and the acrosome intep'ty of semen from four boars frozen with a programmable freezin machine, in mini-(0.25 ml), maxi-(5 ml) plastic straws and in 10 × 5 cm PVC- or Teflon FEP-plastic bags (0.35 – 0.12 mm thick, 5 ml) was studied. The freezing of the semen was monitored using thermocouples placed in the straws and the bags. The freezing curve started from +5°C, at a rate of −3°C/min, to – 6°C, it was held for 1 min at −6°C, and was followed by further drop to −100°C at a rate of −20°C/min, with subsequent storage in LN2. The bags had a much shorter freezing point plnteau, compared to the maxi-straws. Post-thaw sperm motility was significantly higher when semen was frozen in mini-straws or in bags than in maxi-straws. The freezing procedure did not cause major acrosomal damages, significantly more normal apical ridges being present in the bags and mini-straws than in the maxi-straws. This in vitro evaluation indicates that the freezing method employed is satisfactory for freezing large volumes of boar semen into plastic bags .  相似文献   
83.
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   
84.
Abstract— Class II+ dendritic cells were widely distributed throughout normal ovine skin in two main locations: a) in or immediately adjacent to the epidermis and epidermal appendages and b) in the vicinity of the blood vessels. They are unlikely to represent a homogeneous population particularly since Langerhans cells, which previously have been found throughout the epidermal appendages, were located only in the epidermis using acetylcholinesterase staining. Following infection with orf virus, a dense mass of closely associated class II+ dendritic cells develops in the exposed necrotising dermis, adjacent to infected hair follicles and under infected degenerating epidermis. These cells interact and appear to form a barrier to invasion, a framework for immune defence and a template for subsequent epidermal repair; they seem to provide the basis of a highly integrated local dermal defence system. Résumé— Des cellules dendritiques de classe II+étaient largement réparties dans la peau ovine normale dans deux principales zones a) dans l'épiderme et les annexes épidermiques ou dans leur voisnage immédiat b) au voisinage des vaisseaux sanguins. Il est peu probable qu'elles représentant une population homogène particulièrement parce que les cellules de Langerhaps, qui ont été découvertes précédemment dans l'ensemble des annexes épidermiques, furent localisées seulement dans l'épiderme en utilisant une coloration à l'acétylcholinesterase. Après une infection par le virus de l'ecthyma, il se forme une masse dense de cellules dendritiques de classe II+étroitement associées, dans le derme nécrotique atteint, adjacente aux follicules pileux infectés et sous l'épiderme dégénératif infecté. Ces cellules interagissent et apparaissent former une barrière à l'invasion, un cadre pour les défenses immunitaires et un patron pour la réparation épidermique ultérieure; elles semblent fournir les bases d'un système de défense dermique local hautement intégré. Zusammenfassung— Klasse II+-Dendritenzellen waren in der gesamten Haut von normalen Schafen in vorwiegend zwei Bereichen verbreitet: a) in oder unmittelbar neben der Epidermis und der epidermalen Anhangsgebiete und b) in dor Nähe dar Blutgefäße. Sie stellen wahrscheinlich keine homogène Population dar, da die Langerhanszellen, die früher übarall in den epidermalen Anhangsgebilden nachgewiesen wurden, bei Acetylcholinesterase-Färbung nur in der Epidermis zu finden waren. Nach einer Orf-Virus-Infektion formiert sich eine dichte Masse aus eng verbundenen Klasse II+-Dendritenzellen in der betroffenen nekrotisierenden Dermis unmittelbar neben den infizierten Haarfollikeln und unter der infizierten, degenerierenden Epidermis. Diese Zellen stehen untereinander in Verbindung und bilden anscheinend eine Barrière gegen die Invasion, ein Gorüst für die Immunabwehr und einen Ausgangs punkt für die anschließenden Reparaturvorgänge in der Epidermis. Sie scheinen als Basis eines hochentwickelten lokalen Abwehrsystems der Haut zu fungieren. Resumen Células dendríticas de class II+ se observaron en gran cantidad en la piel de la oveja especialmente en dos localizaciones: a) en la epidermis, en la dermis muy próxima a la epidermis y en anejos cutáneos y b) en las proximidades de los vasos sanguíneos. No parece tratarse de una población homogénea de células puesto que las células de Langerhans, que previamente se habían encontrado en los anejos epidérmicos, se encontraron únicamente en la epidermis utilizando técnicas de detección del acetilcol-inesterasa. Después de la infección con el virus del ectima contagioso ovino se observó una masa de células dendríticas de clase II, dispuestas de forma muy densa, en las proximidades de la dermis necrosada y de los folículos pilosos y de la epidermis infectada. Eatas células interaccionan entre si y parecen formar una barrera contra la invasión, una red inmunitaria de defensa y participar en la reparación de la epidermis; parece ser que esta población de células dendriticas son la base de un sistema de defensa dérmico local altamente integrado.  相似文献   
85.
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   
86.
The activity of rat liver glutathione-insulin transhydrogenase (GIT) was measured by HPLC. The degradation of fluorescein isothiocyanate-I (FITC-I)-labeled insulin is separated into several peaks, which are bound different amount of FITC-I. We selected mono-fluorescein-thiocarbamylated insulin to estimate the decrease of insulin content and it became possible to assay GIT activity. This novel method was time-saving and simple, and this system could utilize instead of previous method.  相似文献   
87.
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   
88.
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   
89.
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   
90.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号