全文获取类型
收费全文 | 66171篇 |
免费 | 3719篇 |
国内免费 | 124篇 |
专业分类
林业 | 2907篇 |
农学 | 2234篇 |
基础科学 | 384篇 |
7498篇 | |
综合类 | 10943篇 |
农作物 | 2343篇 |
水产渔业 | 3025篇 |
畜牧兽医 | 35759篇 |
园艺 | 785篇 |
植物保护 | 4136篇 |
出版年
2018年 | 960篇 |
2017年 | 1019篇 |
2016年 | 910篇 |
2015年 | 852篇 |
2014年 | 930篇 |
2013年 | 2830篇 |
2012年 | 1860篇 |
2011年 | 2231篇 |
2010年 | 1419篇 |
2009年 | 1410篇 |
2008年 | 2124篇 |
2007年 | 2065篇 |
2006年 | 1939篇 |
2005年 | 1823篇 |
2004年 | 1679篇 |
2003年 | 1721篇 |
2002年 | 1643篇 |
2001年 | 2006篇 |
2000年 | 1988篇 |
1999年 | 1661篇 |
1998年 | 690篇 |
1997年 | 700篇 |
1996年 | 628篇 |
1995年 | 701篇 |
1994年 | 651篇 |
1993年 | 636篇 |
1992年 | 1343篇 |
1991年 | 1499篇 |
1990年 | 1387篇 |
1989年 | 1396篇 |
1988年 | 1259篇 |
1987年 | 1248篇 |
1986年 | 1290篇 |
1985年 | 1291篇 |
1984年 | 1042篇 |
1983年 | 965篇 |
1982年 | 623篇 |
1979年 | 980篇 |
1978年 | 760篇 |
1977年 | 765篇 |
1976年 | 756篇 |
1975年 | 773篇 |
1974年 | 934篇 |
1973年 | 906篇 |
1972年 | 875篇 |
1971年 | 798篇 |
1970年 | 839篇 |
1969年 | 789篇 |
1968年 | 695篇 |
1967年 | 690篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
A urinary bladder mass in a 12-year-old spayed female West Highland White Terrier was diagnosed after exploratory surgery and biopsy as a transitional cell carcinoma. Four months later the dog presented with an ulcerated plaque-like cutaneous lesion at the previous surgical incision site; concurrent inguinal lymphadenopathy and recurrence of the urinary bladder mass were identified. Transitional cell carcinoma was diagnosed at all 3 sites. Although a definitive relationship cannot be established between the initial surgery for urinary bladder mass and the resultant subcutaneous lesion, surgical implantation should be considered as a source for the neoplastic cells. 相似文献
22.
23.
Field experiments were conducted to determine the direct and residual contributions of legumes to the yield and nitrogen (N) uptake of maize during the wet seasons of 1994 and 1995 at the University Farm, Abubakar Tafawa Balewa University, Bauchi, Nigeria, located in the Northern Guinea savannah of Nigeria. Nodulating soybean, lablab, green gram and black gram contributed to the yield and N uptake of maize either intercropped with the legumes or grown after legumes as a sole crop. Direct transfer of N from the nodulating soybean, lablab, green gram and black gram to the intercropped maize was 24.9–28.1, 23.8–29.2, 19.7–22.1 and 18.4–18.6 kg N ha–1 , respectively. However, the transfer of residual N from these legumes to the succeeding maize crop was 18.4–20.0, 19.5–29.9, 12.0–13.7 and 9.3–10.3 kg N ha–1 , respectively. Four years of continuous lablab cropping resulted in yields and N uptake of the succeeding maize crop grown without fertilizer N that were comparable to the yields and N uptake of the succeeding maize crop supplied with 40–45 kg N ha–1 and grown after 4 years of continuous sorghum cropping. It may therefore be concluded that nodulating soybean, lablab, green gram and black gram may be either intercropped or grown in rotation with cereals in order to economize the use of fertilizer N for maize production in the Nigerian savannah. 相似文献
24.
Jennifer B. Grimm DVM MS Kurt A. Grimm DVM MS Stephen K. Kneller DVM MS William J. Tranquilli DVM MS Sonia S. Crochik DVM MS Matthew G. Bischoff DVM Jennifer L. Podolski DVM 《Veterinary radiology & ultrasound》2001,42(5):458-462
The effects of intramuscularly administered medetomidine and butorphanol (MB), and medetomidine, butorphanol, atropine (MBA) on glomerular filtration rate (GFR) were determined in six dogs as measured by 99m-Tc-labeled diethylenetriaminepentaacetic acid (99mTc-DTPA) nuclear scintigraphy. Direct systolic, diastolic, and mean arterial blood pressures and heart rate were measured at regular time intervals before, during, and after GFR calculations. The mean GFR measurement following MB was significantly greater (4.44 ml/min/kg) than following MBA (3.82 ml/min/kg) or saline treatment (3.41 ml/min/kg). There was no significant difference between the mean GFR measurements following MBA injection and following saline injection. Diastolic and mean arterial pressures following MBA injection were significantly higher than the values recorded after either MB or saline alone. Heart rate following MB administration was significantly lower than that recorded for dogs receiving MBA or saline alone. The results of this study indicate that the administration of medetomidine in combination with butorphanol significantly increases total GFR in healthy dogs, while the administration of the combination of medetomidine, butorphanol, and atropine does not. 相似文献
25.
Abstract – The reproductive biology of three species of rainbowfish (Melanotaeniidae) in northeastern Australian rainforest streams was investigated. Two species, Melanotaenia eachamensis and Cairnsichthys rhombosomoides are endemic to the area, whereas the third, M. splendida splendida, is more widespread. The species were all highly fecund, producing many hundreds of eggs between 1.10 and 1.24 mm in diameter. Melanotaenia eachamensis was the most fecund, produced the largest eggs of the three species, and consequently exhibited the greatest maternal investment (as measured by gonadosomatic index). The majority of reproductive effort occurred during the dry season, although reproductively active fish were present year-round for each of the species, but particularly so for M. s. splendida and C. rhombosomoides. No evidence for a role by temperature or photoperiod as environmental cues for reproduction was found, and it was suggested that gonad development was strongly tied to somatic growth. The concentration of reproduction to the dry season ensures that larvae are produced during a period of relatively stable and benign physical conditions. Comparison of temporal changes in gonadosomatic index values suggest that the spawning season of M. eachamensis , which occurs in high-elevation streams, is more restricted and commences about 1 month earlier than either other species. A similar phenology was observed for the M. s. splendida population found at high elevation and highlights the potential for spatial differences in stream productivity to influence life history. Note 相似文献
26.
Asymmetric illumination contrast: a method of image formation for video light microscopy 总被引:4,自引:0,他引:4
B Kachar 《Science (New York, N.Y.)》1985,227(4688):766-768
Images with high resolution and exceptionally broad gray scale can be obtained by the application of video contrast enhancement to an optimized procedure for imaging transparent objects with oblique rays of illumination. This technique is simple to set up. A conventional microscope with a light source whose position can be adjusted and a video camera with controls for gain and black level are the only essential components. Features such as high resolution, optical sectioning, control of contrast, and operation under low light intensity make this technique preferable, in several instances, to currently used video microscopy techniques. 相似文献
27.
Washed and unwashed red blood cells (RBC) from young calves, adult cattle, hamsters and humans were incubated with Leptospira interrogans serovars pomona and ballum. Washed cells suspended in saline were always haemolysed while unwashed cells and those which were washed and resuspended in plasma were never haemolysed, despite the presence of large numbers of organisms within the culture supernatant. Pomona produced greater haemolysis of cattle and human RBC than did ballum, but with hamster RBC ballum produced greater haemolysis than did pomona. A group of 6- to 9-month-old cattle infected with pomona showed no signs of clinical disease and RBC taken from them before infection and during the development of antibodies to pomona were haemolysed by pomona only after the cells were washed. Plasma therefore appears to have a protective function. This in vitro protective function of plasma even extended to plasma from young seronegative calves. 相似文献
28.
29.
30.