全文获取类型
收费全文 | 9687篇 |
免费 | 653篇 |
国内免费 | 51篇 |
专业分类
林业 | 631篇 |
农学 | 467篇 |
基础科学 | 85篇 |
1728篇 | |
综合类 | 650篇 |
农作物 | 519篇 |
水产渔业 | 786篇 |
畜牧兽医 | 4469篇 |
园艺 | 157篇 |
植物保护 | 899篇 |
出版年
2023年 | 89篇 |
2022年 | 165篇 |
2021年 | 304篇 |
2020年 | 302篇 |
2019年 | 370篇 |
2018年 | 342篇 |
2017年 | 360篇 |
2016年 | 364篇 |
2015年 | 257篇 |
2014年 | 354篇 |
2013年 | 556篇 |
2012年 | 572篇 |
2011年 | 620篇 |
2010年 | 314篇 |
2009年 | 343篇 |
2008年 | 497篇 |
2007年 | 498篇 |
2006年 | 423篇 |
2005年 | 401篇 |
2004年 | 373篇 |
2003年 | 323篇 |
2002年 | 369篇 |
2001年 | 259篇 |
2000年 | 252篇 |
1999年 | 209篇 |
1998年 | 65篇 |
1997年 | 69篇 |
1996年 | 56篇 |
1995年 | 55篇 |
1994年 | 42篇 |
1993年 | 41篇 |
1992年 | 82篇 |
1991年 | 58篇 |
1990年 | 66篇 |
1989年 | 69篇 |
1988年 | 65篇 |
1987年 | 57篇 |
1986年 | 48篇 |
1985年 | 59篇 |
1984年 | 41篇 |
1983年 | 45篇 |
1982年 | 30篇 |
1980年 | 26篇 |
1979年 | 39篇 |
1978年 | 21篇 |
1977年 | 21篇 |
1974年 | 23篇 |
1973年 | 25篇 |
1972年 | 24篇 |
1970年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 625 毫秒
891.
Por S. Mello Dias P. Pinto Silva V. J. M. Campos A. M. Orsi M. C. Oliveira Dayoub R. M. Define 《Anatomia, histologia, embryologia》1983,12(4):347-352
In the literature reviewed, there are certain differences of opinion with regard to the formation and tributareis to the ureter. Therefore, dissection of 40 fowls injected with neoprene latex, k neoprene latex and celobar (radiopaque mass) and vinyl acetate casts through the ureter and blood vessels revealed the formation and disposition of the tributaries to the ureter, and its origin and number of collectors. The results were described in relation to the renal lobes. 相似文献
892.
893.
The kinetics of isotopic exchange of phosphate on hydroxyapatite, amorphous aluminium phosphate, phosphate-treated aluminium oxide and dicalcium phosphate dihydrate were studied in aqueous suspensions as a function of solid/solution ratio and amount of added isotope. The tracer exchange reaction was independent of time for the dicalcium phosphate due to a very small amount of exchangeable phosphate found in the solid and to the high solubility of the material. For the other phosphates, a power function and/or a function composed of a series of exponential terms were found suitable for representing the tracer kinetics. The theoretical background for both functions is shown to be approximately the same. Both describe tracer kinetics for a system containing more than one solid phase. The amounts of exchangeable P were found to depend strongly on the solid/solution ratio but not on the amount of radioactivity added. The dependence of the tracer kinetics on the solid/solution ratio is due to the ageing processes that give rise to the formation of surface layers having physical and chemical properties different from those of the bulk solid. 相似文献
894.
A serological study, using the indirect haemagglutination test, of an outbreak of toxoplasmosis in a flock of blackface sheep is described. The serological aspects of the disease are discussed with reference to this incident, and possible sources of infection are suggested. 相似文献
895.
E de Madron C Prymak J Hendricks 《Journal of the American Veterinary Medical Association》1987,191(3):324-326
A dog was examined because of cardiac tamponade secondary to pericardial effusion. Masses adjacent to the right atrial and ventricular walls were revealed by echocardiography. Pericardectomy and biopsies of the masses established the diagnosis of idiopathic hemorrhagic pericardial effusion with organized thrombi. The dog was healthy 3 months after surgery. These organized thrombi mimicked cardiac neoplasia echocardiographically, and such a possibility should be included in the list of differential diagnoses of cardiac masses. 相似文献
896.
F Baum A de Lahunta E J Trotter 《Journal of the American Veterinary Medical Association》1992,201(8):1222-1224
An 18-month-old neutered male Rottweiler was examined because of slowly progressive spastic tetraparesis and ataxia. Signalment and clinical signs were suggestive of 2 neuronal degenerative diseases presumed to be inherited in young Rottweilers: leukoencephalomyelopathy and neuroaxonal dystrophy. Myelography revealed an extradural compression at the articulation of the second and third cervical vertebrae. At surgery, focal hypertrophy of the yellow ligament was observed to compress the spinal cord ventrally at that site. 相似文献
897.
J. C. Andreo V. D. Pai J. A. C. Navarro J. A. DE Oliveira 《Anatomia, histologia, embryologia》1994,23(3):226-231
Fiber types distribution in the diagastric muscle of tufted capuchin monkey was studied by means of NADH-TR, myosin-ATPase, after alkaline and acid preincubations and SDH histochemical reactions. Three different types of fibers were found presenting an equal distribution. The percentage and types of fibers were as follow: 18.2 % SO (Slow Oxydative), 38.4 % FOG (Fast Oxydative Glycolytic) and 43.4 % FG (Fast Glycolytic). FG fibers revealed the largest area. The relatively high concentration of fast twitch (81.2 %) seems to indicate this muscle is involved with the acceleration and fast speed of jaw movements. Aerobic metabolism represented by SO + FOG fibers (56.6 %) suggestes that this muscle possesses an additional role than that related to the lowering of the jaw. 相似文献
898.
In 29 domestic hens, four blood samples were collected during the period of egg formation, at time points representing different metabolic stages. Plasma concentrations of total calcium, total phosphorus, inorganic phosphorus and total protein were measured, and the effect of adding oyster shell particles to a standard laying diet was investigated. Analyses of covariance were made and correlations between the plasma characteristics were calculated. The following were significantly correlated: total and inorganic phosphorus, calcium and total phosphorus, and calcium and protein. Each of the four characteristics showed a significant decrease during egg formation. Inorganic phosphorus reached a peak 15 h after ovulation, probably related to medullary bone resorption. Plasma total phosphorus differed significantly between chickens. Addition of oyster shell to the diet did not affect the concentration or the pattern of the plasma characteristics during egg formation and did not reduce calcium mobilisation from medullary bone during shell formation. 相似文献
899.
D T de Waal J van Heerden F T Potgieter 《The Onderstepoort journal of veterinary research》1987,54(4):561-568
Serologically negative horses, as determined with the indirect fluorescent antibody test (IFA), were infected with Babesia equi and 60 days later with Babesia caballi. The only clinical signs of disease observed in these animals were a febrile reaction and slight icterus. Haematological changes included a drop in haematocrit and haemoglobin concentration, as well as lowered platelet counts. The serum concentrations of albumin, iron and phosphorus were lowered. Mildly elevated serum bilirubin and fibrinogen concentrations were observed. Antibody titres were determined with the IFA and complement fixation (CF) tests. Antibodies to B. equi were first detected between Days 10-19 and 12-38 with the IFA and CF test, respectively, while the corresponding IFA periods for B. caballi were 6-8 days after infection. The parasitaemia of both B. equi and B. caballi infections never reached the 1% level. 相似文献
900.
N A de Visser H J Breukink F G van Zijderveld P W de Leeuw 《The Veterinary quarterly》1987,9(4):289-296
Forty-five calves on four veal calf units were monitored during the first four weeks after their arrival. Faecal samples were collected on alternate days and screened for the presence of rotaviruses, bovine coronavirus, Cryptosporidium oocysts, K99 positive strains of E. coli and Salmonella spp. Rotaviruses and Cryptosporidium were the most commonly detected agents (78% and 60% respectively of the calves). Bovine coronavirus was detected in the faeces of 18% of the calves, whilst K99 positive E. coli was only found in 2 samples from one calf. Salmonella spp. were not isolated from any of the 646 faecal samples examined. Shedding of rotaviruses occurred in a bimodal pattern beginning in the first week of the survey. Cryptosporidium oocysts were detected most frequently in the interval between the two peaks of rotavirus shedding. The presence of rotaviruses or Cryptosporidium oocysts in faeces was not strongly associated with scour, nor were combined infections with these agents or the cases of bovine coronavirus infection. The condition of the calves throughout the survey was generally satisfactory. 相似文献