全文获取类型
收费全文 | 19270篇 |
免费 | 154篇 |
国内免费 | 1篇 |
专业分类
林业 | 3697篇 |
农学 | 1372篇 |
基础科学 | 143篇 |
3164篇 | |
综合类 | 1242篇 |
农作物 | 2419篇 |
水产渔业 | 1988篇 |
畜牧兽医 | 2258篇 |
园艺 | 1140篇 |
植物保护 | 2002篇 |
出版年
2022年 | 39篇 |
2021年 | 70篇 |
2020年 | 32篇 |
2019年 | 42篇 |
2018年 | 2789篇 |
2017年 | 2741篇 |
2016年 | 1226篇 |
2015年 | 126篇 |
2014年 | 105篇 |
2013年 | 141篇 |
2012年 | 953篇 |
2011年 | 2317篇 |
2010年 | 2190篇 |
2009年 | 1342篇 |
2008年 | 1462篇 |
2007年 | 1739篇 |
2006年 | 179篇 |
2005年 | 248篇 |
2004年 | 232篇 |
2003年 | 276篇 |
2002年 | 156篇 |
2001年 | 77篇 |
2000年 | 111篇 |
1999年 | 48篇 |
1998年 | 15篇 |
1997年 | 24篇 |
1996年 | 17篇 |
1994年 | 17篇 |
1993年 | 22篇 |
1992年 | 34篇 |
1991年 | 34篇 |
1990年 | 39篇 |
1989年 | 34篇 |
1988年 | 35篇 |
1987年 | 34篇 |
1986年 | 33篇 |
1985年 | 35篇 |
1984年 | 25篇 |
1983年 | 25篇 |
1979年 | 21篇 |
1978年 | 15篇 |
1977年 | 25篇 |
1976年 | 14篇 |
1974年 | 20篇 |
1973年 | 27篇 |
1972年 | 19篇 |
1971年 | 16篇 |
1970年 | 21篇 |
1969年 | 22篇 |
1968年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Michael J. A. Young Arlo W. Fast Paul G. Olin 《Journal of the World Aquaculture Society》1989,20(1):7-11
Chinese catfish ( Clarias fuscus ) were successfully spawned in Hawaii using human chorionic gonadotropin (HCG) at dosage rates of two and four international units (IU) per gram body weight. Fish not injected with HCG did not produce viable eggs. Successful spawns with HCG occurred between May and October. Hatch rates of up to 80% were obtained during June, July, and August for those fish given either a 2 or 4 IU per gram body weight injection of HCG. Fish spawned in either May or October yielded significantly higher hatch rates when injected with 4 rather than 2 IU per gram body weight. Fish held at elevated temperatures (28 to 30 C) prior to the normal spawning season developed significantly larger oocyte diameters, 60 days earlier than fish held under ambient temperature conditions (21.5 to 24 C). Photoperiod manipulation at ambient temperature conditions was associated with earlier oocyte maturation, but photoperiod effects were much less important than temperature. 相似文献
2.
3.
Hemagglutination and hemagglutination inhibition of turkey red blood cells with Mycoplasma hyopneumoniae 总被引:2,自引:0,他引:2
T F Young B Z Erickson R F Ross Y Wannemuehler 《American journal of veterinary research》1989,50(7):1052-1055
The ability of Mycoplasma hyopneumoniae to agglutinate RBC was evaluated to develop an in vitro cytadsorption assay. Using swine RBC in a microtitration hemagglutination test, no agglutination or partial agglutination was detected. Comparison of RBC from various other species indicated that improved hemagglutination was obtained with RBC from turkeys. This hemagglutination was detected only when mycoplasma cells used in the assay had been frozen and thawed, heated at 50 C for 30 minutes, or treated with trypsin. Treatment of RBC with trypsin or neuraminidase enhanced hemagglutination. Possible surface lectin activity in M hyopneumoniae was evaluated by use of carbohydrates in a blocking assay; hemagglutination was not inhibited by any of 13 carbohydrates evaluated. Mycoplasma hyopneumoniae convalescent porcine serum and monoclonal antibodies against 2 M hyopneumoniae immunogens of molecular weights of 64,000 and 41,000 inhibited hemagglutination. 相似文献
4.
L.E. Young D.H. Bartram M. Diamond A. Gregg R.S. Jones 《Veterinary anaesthesia and analgesia》1991,18(Z1):171-174
5.
Four hundred and ninety horses were anaesthetised with halothane for clinical surgical or diagnostic procedures following induction with either detomidine/keta-mine, detomidine/thiopentone, xylazine/ketamine or guaiphenesin/thiopentone. Routine clinical monitoring was performed during anaesthesia. All horses developed hypotension (mean arterial pressures below 80 mm Hg) and respiratory depression (significant fall in respiratory rate and arterial carbon dioxide tension above 7 kPa (53 mm Hg)) consistent with the recognised effects of halothane. All anaesthetic procedures incorporating xylazine or detomidine resulted in lower pulse rates (28–35 per min) than after guaiphenesin/thiopentone (36–44 per min) and there was greater respiratory depression after techniques employing thiopentone rather than keta-mine. Development of hypotension was delayed after techniques using the α2 adrenoceptor agonist agents (xylazine and detomidine), particularly detomidine. Prernedication with acepromazine did not affect any of the physiological variables measured after techniques employing detomidine. Recovery to standing was fastest after xylazine/ketamine (31±1 min) and slowest after detomidine/thiopentone (53±2 min). Recovery quality was best after detomidine/thiopentone and all techniques employing an α2 adrenoceptor agonist agent resulted in smoother recovery than after guaiphenesin/thiopentone. This study demonstrates that most of the physiological effects of individual induction agents are overridden by the cardiovascular and respiratory depressant effects of halothane. The study also shows that detomidine is an acceptable sedative for use before general anaesthesia with halothane in horses. 相似文献
6.
Clark RG Henderson HV Hoggard GK Ellison RS Young BJ 《New Zealand veterinary journal》1987,35(8):126-133
Blood samples from 433 periparturient recumbent cows submitted by veterinary practitioners to Ruakura Animal Health Laboratory during 1983 and 1984 were analysed and results related to whether cows recovered, died or were euthanased. Generally cows were sampled only once and the time varied from 15 minutes to 20 days after becoming recumbent. During 1983 serum calcium, magnesium, phosphorus, creatine phosphokinase (CK), aspartate amino transferase (AST), glutamate dehydrogenase (GDH), gamma glutamyl transferase (GGT) were analysed. In 1984 serum urea, creatinine, fibrinogen and haematological examination (haemoglobin, haematocrit, total and differential white cell counts) were added to the panel. Overall 39% of cows recovered, 30% died and 32% were destroyed. Precalving cows had 111% more deaths and 7% less survivors than postcalving recumbent cows (P<0.1). There was little difference (3%) in euthanasia prevalence. Tests that were most useful in predicting a lack of recovery were serum urea and muscle enzymes. Using these tests and duration of recumbency when sampled a model was produced to predict the probability of recovery from 254 cases. 相似文献
7.
8.
Scanning electron microscope study of Sendai virus fusion between HeLa cells and chick erythrocytes.
Chick erythrocytes were fused with HeLa cells by Sendai virus and preparations examined by scanning electron microscopy at different times after fusion. Heterokaryons were usually formed by fusion of erythrocyte ghosts with HeLa cells. Occasionally whole erythrocytes were engulfed but there was no evidence that free nuclei fused. Initial inter-cell attachments were usually, and possibly always, made at the site of an attached virus particle. This study helps to correlate topographical findings with previous two-dimensional studies with the transmission electron microscope and may also provide a model system for the fusion of parasitised erythrocytes with eukaryotic cells. 相似文献
9.
Hyun-Young Cho 《Pesticide biochemistry and physiology》2005,83(1):29-36
The structural gene for glutathione S-transferase in Oryza sativa was successfully cloned from a cDNA library by the polymerase chain reaction method. The deduced amino acid sequence of this gene showed 44-66% similarity to the sequences of the class phi GSTs from Arabidopsis thaliana and Zea mays. This gene was expressed in Escherichia coli with the pET vector system and the gene product was purified to homogeneity by GSH-Sepharose affinity column chromatography. The expressed OsGSTF3-3 was a homo-dimer composed of 24 kDa subunit and its pI value was approximately 7.3. The OsGSTF3-3 was retained on GSH affinity column and its Km value for GSH was 0.28 mM. The OsGSTF3-3 displayed high activity toward 1-chloro-2,4-dinitrobenzene, a general GST substrate and also had high activities towards acetanilide herbicides, alachlor, and metolachlor. The OsGSTF3-3 was highly sensitive to inhibition by benastatin A and S-hexyl-GSH. From these results, the expressed OsGSTF3-3 is a phi class GST and seems to play an important role in the conjugation of the chloroacetanilide herbicides. 相似文献
10.
SR Cho SA Ock JG Yoo B Mohana kumar SY Choe GJ Rho 《Reproduction in domestic animals》2005,40(2):171-176
The present study was designed to examine the effects of cell-cycle synchronization protocols, such as confluent, roscovitine treatment and serum starvation, in bovine foetal fibroblasts on synchronization accuracy at G0/G1, viability, apoptosis, necrosis and ploidy for use as a nuclei donor. The cells in 5-10 passages were randomly allocated into three treated groups. Cells were cultured either in Dulbecco's modified Eagle's medium (DMEM) + 10% foetal bovine serum (FBS) until 90% confluent (group 1, confluent), in DMEM + 10% FBS + 30 microM roscovitine for 12 h (group 2, roscovitine), or in DMEM + 0.5% FBS for 5 days (group 3, serum starvation). Most of the cells (>80%) in all groups were arrested at the G0/G1 stage. Although the rates did not differ, cells in group 1 showed an increased cell population arrested at the G0/G1 phase. Significantly (p < 0.05) higher rates of apoptosis occurred in group 3 than in group 1 and 2 (10% vs 6% and 6%, respectively). No differences in chromosomal abnormality were observed among groups. However, by increasing the number of cell culture passages up to 15, significantly (p < 0.05) higher chromosomal abnormality was observed than in 5 and 10 passages (39% vs 28% and 23%, respectively) in group 1. The results clearly indicated that bovine foetal fibroblasts could be effectively synchronized at G0/G1 stages by all the three different treatments, confluent, roscovitine and serum starvation. However, cells in confluent showed reduced apoptosis and necrosis when they underwent 5-10 passages, exhibiting increased percentage of cells with stable chromosome diversity. Hence, cells in confluent merit further studies before they could be used as nuclear donors. 相似文献