全文获取类型
收费全文 | 265727篇 |
免费 | 15083篇 |
国内免费 | 655篇 |
专业分类
林业 | 23669篇 |
农学 | 14002篇 |
基础科学 | 2969篇 |
43012篇 | |
综合类 | 28999篇 |
农作物 | 17289篇 |
水产渔业 | 16708篇 |
畜牧兽医 | 104717篇 |
园艺 | 6305篇 |
植物保护 | 23795篇 |
出版年
2020年 | 2843篇 |
2019年 | 3647篇 |
2018年 | 3908篇 |
2017年 | 4310篇 |
2016年 | 4722篇 |
2015年 | 4297篇 |
2014年 | 5635篇 |
2013年 | 16237篇 |
2012年 | 6289篇 |
2011年 | 8257篇 |
2010年 | 7309篇 |
2009年 | 7842篇 |
2008年 | 7680篇 |
2007年 | 6647篇 |
2006年 | 7283篇 |
2005年 | 6521篇 |
2004年 | 6465篇 |
2003年 | 6172篇 |
2002年 | 5561篇 |
2001年 | 6353篇 |
2000年 | 6104篇 |
1999年 | 5527篇 |
1998年 | 4155篇 |
1997年 | 4224篇 |
1996年 | 3973篇 |
1995年 | 4640篇 |
1994年 | 4057篇 |
1993年 | 3737篇 |
1992年 | 4764篇 |
1991年 | 5014篇 |
1990年 | 4698篇 |
1989年 | 4653篇 |
1988年 | 4159篇 |
1987年 | 4280篇 |
1986年 | 4320篇 |
1985年 | 4528篇 |
1984年 | 4084篇 |
1983年 | 3876篇 |
1982年 | 3075篇 |
1981年 | 2965篇 |
1980年 | 2920篇 |
1979年 | 3568篇 |
1978年 | 3169篇 |
1977年 | 2799篇 |
1976年 | 2694篇 |
1975年 | 2551篇 |
1974年 | 2887篇 |
1973年 | 2922篇 |
1972年 | 2662篇 |
1971年 | 2628篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Several investigators have suggested that the blood-vessel system in the equine periodontal ligament does not only serve nutritional needs, but also specific functional needs, e.g. in terms of a shock absorbing system. In order to supplement the previous data, corrosion casts of the periodontal blood vessels were studied with special attention to the spatial arrangement and connections of the vessels. The heads of eight warm-blooded horses (age 2.5–23 years, seven female, one male), which had been killed for medical reasons, were dissected. The arteria alveolaris inferior and the a. infraorbitalis were perfused with 100 ml Heparin (20 000 IU) followed by 100 ml tap water. After storage at 4°C for 24–96 h, 10–200 ml methacrylate resin (BiodurTM E20) were injected by use of a cartridge pistol for approx. 1 h. After polymerization for 24 h at 60°C, the jaws were frozen and cut with a steel band saw in a horizontal, sagittal or transversal plane to obtain segments that exposed the periodontal space. The specimens were macerated in detergent at 60°C until the soft tissues had vanished. Care was taken to keep the periodontal vessels complete and in topographical integrity. The vascular casts were mesoscopically examined by use of a dissection microscope (magnification 5.8×–40×). The blood vessels in the periodontal space connected with vessels in three other sites:
- (1)
occlusal – with the blood vessels of the gingiva;
992.
993.
Kevin Kline PhD Leonard P. Frey PhD Jonathan H. Foreman DVM MS Joseph T. Lyman DVM MS 《Journal of Equine Veterinary Science》2005,25(8):349-354
Changes in blood gases, pH, and plasma electrolyte concentrations in response to intravenously infused sodium bicarbonate (NaHCO3) and sodium acetate (NaCH3CO2) solutions (1.34 mEq/mL) in 5 light breed mares were investigated. Jugular venous blood samples were collected before and after completion of the infusions in 20-minute intervals for 200 minutes. Infusion of sodium bicarbonate and sodium acetate caused significant (P < .00l) increases in blood pH and bicarbonate ion concentration that persisted throughout the collection period. The elevation in blood pH and bicarbonate ion concentrations was greater (P < .01) for sodium bicarbonate than for sodium acetate immediately after the completion of the infusions but was not different (P > .05) thereafter. There were significant reductions (P < .01) in plasma-ionized calcium and potassium after infusion of both sodium bicarbonate and sodium acetate. This study found that significant metabolic alkalosis in horses and corresponding shifts in electrolyte concentrations can be induced by intravenous infusion of solutions of either sodium bicarbonate or sodium acetate, and they persist for at least 3 hours. These data show that the short-term elevation in pH and bicarbonate ion concentration is momentarily higher after infusion of sodium bicarbonate. This is likely due to the direct infusion of bicarbonate ions in the sodium bicarbonate treatment, such that further metabolism is not required to be effective. However, the longer-term alkalosis did not differ between isomolar solutions of sodium bicarbonate and sodium acetate. 相似文献
994.
995.
996.
Forty Swiss Large White piglets of 4 weeks of age were used to determine the effect of dietary Chinese rhubarb on growth performance, as well as on energy and nitrogen metabolism by means of indirect respiration calorimetry studies. A cereal-based diet, supplemented with four different dosages of Chinese rhubarb (0.0%, 0.25%, 0.5%, 1%), was offered ad libitum to the piglets. Gaseous exchange was measured, and urine, faeces, and blood samples were taken. The addition of 0.25% dietary rhubarb increased feed intake (+32%) and daily weight gain (+67%) compared to the diet containing the greatest amount of rhubarb (1%). The piglets fed diet supplemented with 0.25% rhubarb digested and metabolised more energy and nitrogen relative to the animals of treatment 1%. As a consequence, the same group (0.25%) converted more energy and nitrogen into body protein than piglets receiving diet supplemented with 1% rhubarb. However, compared to the control group, the addition of 0.25% rhubarb to the diet resulted in not significantly alter growth performance, energy, and nitrogen metabolism of the animals.Blood parameters were not affected by the rhubarb supplementation. The dose-responding effect of Chinese rhubarb was reflected by the dry matter content of faecal samples. According to the laxative effect of higher doses of rhubarb, the addition of 1% rhubarb to the diet reduced dry matter content of faeces. This effect was well visible in practice, although not relevant in statistical terms. The addition of 0.5% dietary rhubarb had no relevant effect on growth performance or on energy and nitrogen metabolism of treated animals. 相似文献
997.
It is unlikely that human beings acquire a zoonotic infection from healthy cats without ectoparasites. The benefits of cat ownership to human mental health are well established. Veterinarians and physicians should work together closely to provide accurate information to cat owners so that logical decisions concerning cat ownership can be made by the owner. 相似文献
998.
999.
A. Costagliola D. Russo A. A. Izzo P. Urbani V.
di
Marzo A. Cecio 《Anatomia, histologia, embryologia》2005,34(Z1):13-13
The endocannabinoid anandamide may regulate intestinal motility through activation of CB1 receptors. Anandamide is then inactivated by fatty acid amide hydrolase (FAAH), a membrane bound enzyme. Under pathological conditions, inactivation of such enzymatic activity may lead to inhibition of the intestinal motility. Here, preliminary reports on the distribution of Fatty Acid Amide Hydrolase (FAAH) immunoreactivity in the mouse gastrointestinal neurons, and the pharmacological effects of N‐arachidonoylserotonin (AA‐5HT), a selective inhibitor of FAAH, are reported. FAAH was revealed by an indirect immunofluorescence. Laminar preparations containing the myenteric or the submucous plexus adhered, were peeled off after the whole gut wall had been stretched out and fixed in 4% paraformaldehyde. They were subsequently incubated with a polyclonal anti‐serum directed against a region near the N‐terminus of the human FAAH and revealed by a FITC‐conjugated goat anti‐rabbit secondary anti‐serum. FAAH‐immunoreactive neurons were observed within the myenteric ganglia throughout the GIT. The positive nerve cells varied in size and density of immunoreactivity. Stomach and large intestine showed the highest neuronal density. AA‐5HT significantly reduced both gastric emptying and gastrointestinal tract transit. Such inhibitory effect was reduced by the C1 receptor antagonist SR141716A. Both morphological and pharmacological results suggest that FAAH may play a critical role in controlling gut anandamide levels. 相似文献
1000.
H. Neubauer L. D. Sprague R. Zacharia H. Tomaso S. Al Dahouk R. Wernery U. Wernery H. C. Scholz 《Zoonoses and public health》2005,52(5):201-205
Burkholderia mallei causes glanders or farcy in solipeds, a disease that must be reported to the OIE (Office International des Epizooties, Paris, France). The number of reported outbreaks has increased steadily during the last decade. Serodiagnosis is hampered by the considerable number of false‐positives and ‐negatives of the internationally prescribed tests. The major problem leading to low sensitivity and specificity of complement fixation test (CFT) and enzyme‐linked immunosorbent assay (ELISA) has been linked to the test antigens currently used, i.e. crude preparations of whole cells. Future perspectives for the development and evaluation of serological test kits using well‐characterized single antigens are discussed in the light of recent molecular research on B. mallei and the closely related saprozoonotic agent B. pseudomallei. 相似文献