全文获取类型
收费全文 | 33966篇 |
免费 | 2200篇 |
国内免费 | 3520篇 |
专业分类
林业 | 1634篇 |
农学 | 2868篇 |
基础科学 | 595篇 |
7923篇 | |
综合类 | 13639篇 |
农作物 | 2646篇 |
水产渔业 | 2194篇 |
畜牧兽医 | 4437篇 |
园艺 | 1088篇 |
植物保护 | 2662篇 |
出版年
2024年 | 187篇 |
2023年 | 760篇 |
2022年 | 1225篇 |
2021年 | 1475篇 |
2020年 | 1509篇 |
2019年 | 1611篇 |
2018年 | 1230篇 |
2017年 | 1851篇 |
2016年 | 2131篇 |
2015年 | 1616篇 |
2014年 | 1810篇 |
2013年 | 2448篇 |
2012年 | 2825篇 |
2011年 | 2591篇 |
2010年 | 2155篇 |
2009年 | 2013篇 |
2008年 | 1737篇 |
2007年 | 1920篇 |
2006年 | 1563篇 |
2005年 | 1243篇 |
2004年 | 911篇 |
2003年 | 709篇 |
2002年 | 543篇 |
2001年 | 516篇 |
2000年 | 401篇 |
1999年 | 421篇 |
1998年 | 305篇 |
1997年 | 282篇 |
1996年 | 250篇 |
1995年 | 247篇 |
1994年 | 179篇 |
1993年 | 185篇 |
1992年 | 171篇 |
1991年 | 159篇 |
1990年 | 114篇 |
1989年 | 115篇 |
1988年 | 84篇 |
1987年 | 69篇 |
1986年 | 38篇 |
1985年 | 19篇 |
1984年 | 8篇 |
1983年 | 7篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1978年 | 8篇 |
1976年 | 3篇 |
1962年 | 6篇 |
1956年 | 4篇 |
1955年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 37 毫秒
81.
82.
退化草地土壤生化活性研究 总被引:3,自引:0,他引:3
通过对三种不同退化程度的退化草地土壤生化活性进行测定和相关性分析,结果表明草地退化后其土壤生化活性受到不同程度的影响,表现为土壤生化活性随着退化程度增高而减小,但差异并非都达到统计学上的显著性,而土壤生化活性间的相关性则显著地与草地退化程度有关,说明退化草地土壤微生物间的协调作用受到显著影响,从而影响土壤氮素和碳素代谢途径。 相似文献
83.
84.
猪血浆蛋白(酶)多态性与杂种优势的关系 总被引:2,自引:0,他引:2
为探讨血浆蛋白 (酶 )多态性与杂种优势的关系 ,测定了杜洛克、长白、大白、杜×长大、大×长大、长×大、大×长共 7个品种 (组合 )的 8个血浆蛋白 (酶 )位点的多态性及部分生长和胴体性状 ,计算了平均基因杂合度与部分经济性状实测值和杂优率的相关关系 .结果表明 ,平均基因杂合度与遗传距离呈正相关 ,与日增重、屠宰率、背膘厚、后腿比例的实测值或杂优率呈正相关 ,与眼肌面积的实测值和杂优率呈负相关 .平均基因杂合度和亲本间遗传距离可为预测杂种优势提供依据 . 相似文献
85.
银杏幼苗叶片转化酶活性及其动力学 总被引:4,自引:0,他引:4
采用波钦诺克XH法研究了田间和室内栽培的银杏幼苗叶片转化酶的活性及其动力学性质。结果表明:银杏幼苗叶片转化酶在pH值5.0、温度55℃时活性最强;该酶的米氏常数为3.7×10-2mol·L-1;室内盆栽的银杏幼苗叶片转化酶的活性显著高于田间栽培的同龄银杏幼苗叶片转化酶的活性。 相似文献
86.
O'Neill S Boothby JT Feldman BF 《Veterinary clinical pathology / American Society for Veterinary Clinical Pathology》1986,15(1):22-26
A competitive enzyme immunoassay has been used to detect and quantitate fibronectin in canine plasma. In this test, purified fibronectin, bound to microtiter plates, competes with plasma fibronectin for the conjugated antibody, rabbit-anticanine, fibronectin-horseradish peroxidase. The assay could detect fibronectin in purified standards from 58 ng/ml to 580 microgram/ml. The range of 1-100 microgram/ml was linear for plasma samples diluted 1:10, allowing samples with fibronectin concentrations from 10-1000 microgram/ml to be easily measured by this method. The mean normal fibronectin concentration of 132 dogs, by this method, was determined to be 320 +/- 74 microgram/ml. 相似文献
87.
J. Rashid D. J. Weiss S. K. Maheswaran M. P. Murtaugh 《Veterinary research communications》1996,20(6):519-531
Local and systemic activation of coagulation is frequently associated with bacterial sepsis. The coagulopathy is due, at least in part, to expression of tissue factor (TF) by monocytes and macrophages. The purpose of this study was to evaluate the expression of procoagulant activity by bovine alveolar macrophages, leukocytes and platelets, and to determine the relative potency of three chemical inhibitors of TF expression (pentoxifylline, retinoic acid, and cyclosporin A). Bovine alveolar macrophages were stimulated with lipopolysaccharide (LPS) derived from Pasteurella haemolytica or recombinant bovine tumour nervous factor (TNF) and dose- and time-dependent effects on TF expression were studied. LPS and TNF induced TF expression in alveolar macrophages and LPS treatment of whole blood induced TF expression in mononuclear cells. Neutrophils and platelets also expressed procoagulant activity, but this activity was not inhibited by anti-bovine TF monoclonal antibody. Pentoxifylline (40 mol/L), retinoic acid (0.01 mmol/L) and cyclosporin A (0.08 mol/L) inhibited TF expression when added concurrently with LPS or TNF, but not when added 4 h after stimulation. TF mRNA was not detected in unstimulated alveolar macrophages by Northern blot analysis. In contrast, exposure to LPS or TNF for 6 h induced marked expression of TF mRNA, which was inhibited by treatment with pentoxifylline, retinoic acid and cyclosporin A. Expression of TNF by alveolar macrophages stimulated with LPS was also inhibited by these compounds. Our results indicate that procoagulant activity expressed by alveolar macrophages and monocytes is associated with expression of TF, whereas procoagulant activity expressed by neutrophils and platelets is not. The concentrations of pentoxifylline and retinoic acid necessary for inhibition of TF expression in vitro may not be achievable in vivo owing to their toxic effects. However, the in vitro concentration of cyclosporin A that inhibited TF expression did not exceed the plasma concentration observed in humans, and therefore may be useful for inhibition of TF expression in vivo.Abbreviations BAL
bronchoalveolar lavage
- LPS
lipopolysaccharide
- cDNA
cloned deoxyribonucleic acid
- cAMP
cyclic adenosine monophosphate
- GAPDH
glyceraldehyde phosphate dehydrogenase
- mRNA
messenger ribonucleic acid
- TF
tissue factor
- TNF
tumour necrosis factor
- DPBS
Dulbecco's phosphate-buffered saline 相似文献
88.
The use of cultured hepatocytes from goats and cattle to investigate xenobiotic oxidative metabolism
C. Montesissa P. Anfossi G. Van't Klooster M. Mengelers 《Veterinary research communications》1996,20(5):449-460
The oxidative metabolism of aldicarb (ALD), a carbamate pesticide, and fenbendazole (FBZ), an anthelmintic, was studied using cultured hepatocytes obtained from 4 goats and a bullock and incubated with ALD (50 mol/L) and FBZ (10 mol/L). The parent compounds and the metabolites were measured by HPLC. Both compounds are metabolized at the sulphur atom via two sequential oxidations, first to the sulphoxide (aldicarb sulphoxide and oxfendazole, respectively) and then to the sulphone. Oxfendazole and fenbendazole sulphone from FBZ, and aldicarb sulphoxide from ALD were found in both species. Aldicarb sulphone was not produced by the hepatocyte preparations from the bullock. The good correlation obtained comparing the in vitro results of FBZ metabolism with published in vivo dat obtained on FBZ kinetics in the same species confirmed the usefulness of in vitro models for predictive analysis of in vivo xenobiotic biotransformations.Abbreviations ALD
aldicarb
- ALDSON
aldicarb sulphone
- ALDSOX
aldicarb sulphoxide
- BSA
bovine serum albumin
- ID
internal diameter
- EGTA
ethylene glycol bis(-aminoethyl ether) N,N,N,N-tetraacetic acid
- FBZ
fenbendazole
- FBZSON
fenbendazole sulphone
- HBSS
Hanks' balanced saline solution
- HPLC
high-pressure liquid chromatography
- LDH
lactate dehydrogenase
- MFO
mixed function oxidase
- NCS
newborn calf serum
- OXF
oxfendazole
- WME
Williams' Medium E 相似文献
89.
G. Tuitert Y. Hofmeester 《European journal of plant pathology / European Foundation for Plant Pathology》1994,100(1):19-53
A field experiment was set up in 1988 to study the development of rhizomania disease of sugar beet at different inoculum levels of beet necrotic yellow vein virus (BNYVV) in soil. Five, tenfold different, inoculum levels were created by addition of the approximate amounts of 0, 0.5, 5, 50 and 500 kg infested soil per ha (the latter corresponding to 0.01% v/v calculated to the tillage layer). A drip irrigation treatment was applied to study the influence of soil moisture on disease. Susceptible sugar beet, cv. Regina, was grown for three consecutive years.In the first year, root symptoms were not observed, but BNYVV-infected plants were detected by ELISA in low numbers at all inoculum levels at harvest. After late drilling in 1989, high numbers of infected plants, up to 90–100% in plots with the highest inoculum level, were detected already in June. Root symptoms were also observed from June onwards. In both these years disease incidence increased in time and was significantly influenced by the initial inoculum level. In the third year, the whole field was heavily diseased, and only for the non-irrigated plots incidence differed for different initial inoculum levels. The expression of symptoms by BNYVV-infected plants was influenced by initial inoculum level, thus by the amount and timing of primary infection.Root weight at harvest was not affected, but sugar content decreased with increasing inoculum level already in 1988, leading to a reduction in sugar yield of 10% at the highest inoculum level. In 1989, both root weight and sugar content decreased progressively with increasing inoculum level, resulting in sugar yield reductions of 11–66% (down to approximately 3000 kg ha–1) for low to high inoculum levels compared to the control. As the control plots became contaminated, all yields were low in 1990, still showing a decrease with increasing inoculum level in the non-irrigated plots, but an overall mean sugar yield of 3323 kg ha–1 for the irrigated ones.Sodium and -amino nitrogen content of the root, additional quality parameters determining extractability of sucrose, showed an increase and decrease, respectively, with increasing initial inoculum level already in the first year. The relative differences in contents compared to those from the control were largest for Na content. A significant negative correlation was found between Na (mmol kg–1 root) and sugar content (% of fresh weight); linear for 1988, exponential for 1989 and 1990.In spring 1989, the infestation of individual plots was assessed using a quantitative bioassay estimating most probable numbers (MPNs) of infective units of BNYVV per 100 g dry soil. The relationship between the MPns determined and root weight, sugar content and sugar yield at harvest could be described by Gompertz curves. The increase in disease incidence with increasing MPN in 1989 was adequately fitted with a logistic equation. 相似文献
90.
Hill D Correa MT Stevens JB 《Veterinary clinical pathology / American Society for Veterinary Clinical Pathology》1994,23(3):73-75
Azostix-reagent-tests(R) strips (Ames, Miles, Inc., Diagnostic Division, Elkhart, IN) were used to measure blood urea nitrogen values in blood samples from 125 dogs and cats at the North Carolina State University, College of Veterinary Medicine. Results of the tests were compared with standard serum urea nitrogen results. Sensitivity, specificity, and negative predictive values were high (86.4, 90.3, and 96.5%, respectively). Positive predictive value was low, 65.5% of the dogs and cats with elevated blood urea nitrogen values were correctly classified as abnormal The test performs well when the prevalence of abnormal values is near 50%. 相似文献