全文获取类型
收费全文 | 2064篇 |
免费 | 121篇 |
国内免费 | 1篇 |
专业分类
林业 | 82篇 |
农学 | 42篇 |
基础科学 | 5篇 |
351篇 | |
综合类 | 295篇 |
农作物 | 106篇 |
水产渔业 | 107篇 |
畜牧兽医 | 1079篇 |
园艺 | 32篇 |
植物保护 | 87篇 |
出版年
2023年 | 18篇 |
2022年 | 17篇 |
2021年 | 32篇 |
2020年 | 45篇 |
2019年 | 54篇 |
2018年 | 47篇 |
2017年 | 44篇 |
2016年 | 53篇 |
2015年 | 37篇 |
2014年 | 60篇 |
2013年 | 94篇 |
2012年 | 119篇 |
2011年 | 188篇 |
2010年 | 73篇 |
2009年 | 69篇 |
2008年 | 140篇 |
2007年 | 122篇 |
2006年 | 116篇 |
2005年 | 144篇 |
2004年 | 143篇 |
2003年 | 115篇 |
2002年 | 115篇 |
2001年 | 30篇 |
2000年 | 17篇 |
1999年 | 11篇 |
1998年 | 15篇 |
1997年 | 15篇 |
1996年 | 14篇 |
1995年 | 17篇 |
1994年 | 21篇 |
1993年 | 10篇 |
1992年 | 17篇 |
1991年 | 15篇 |
1990年 | 10篇 |
1989年 | 5篇 |
1988年 | 5篇 |
1987年 | 9篇 |
1986年 | 9篇 |
1985年 | 10篇 |
1984年 | 8篇 |
1983年 | 8篇 |
1982年 | 7篇 |
1980年 | 6篇 |
1977年 | 5篇 |
1975年 | 5篇 |
1972年 | 6篇 |
1967年 | 5篇 |
1966年 | 7篇 |
1959年 | 4篇 |
1953年 | 5篇 |
排序方式: 共有2186条查询结果,搜索用时 671 毫秒
991.
Clayton R. Butterly Petra Marschner Ann M. McNeill Jeff A. Baldock 《Biology and Fertility of Soils》2010,46(7):739-753
An incubation study determined the effect of one dry–rewetting (DRW) event on the turnover of carbon (C), phosphorus (P) and
nitrogen (N). Thirty-two soils were collected from different climatic regions of southern Australia, varying in soil type,
land use and agronomic management history. We hypothesised that respiration and nutrient pulses are related to soil physio-chemical
properties. Respiration (CO2 release) was measured intensively for 90 h after rewetting. C mineralisation (C
min) model fitting was used to describe the amount of mineralisable C (Co90 h) and the proportional mineralisation rate (k). Compared to constantly moist soils, 13 soils showed increases in both Co90 h and k, indicating that DRW increased the amount of mineralisable C and the rate at which C was mineralised over the 90-h period.
In 17 soils, k was increased but not Co90 h, showing an increase in C mineralisation rate but no change in the amount of mineralisable C. Two soils showed a reduction
in k with no change in Co90 h, possibly due to low C contents and small microbial biomass. Only one soil exhibited no change in either Co90 h or k. Multiple linear regression analysis indicated that the magnitude of the increase in mineralisable C in response to the DRW
event (∆Co90 h = Co90 h DRW − Co90 h moist) was primarily explained by clay content (39%); however, inclusion of nine soil physio-chemical properties explained
more of the variation in ∆Co90 h than any of the properties alone. Five of the nine physio-chemical variables present in the multiple-regression model were
related to C content or composition. Pulses in available N and P were not related to ∆Co90 h. 相似文献
992.
993.
ACVIM small animal consensus statement on Lyme disease in dogs: diagnosis, treatment, and prevention
Littman MP Goldstein RE Labato MA Lappin MR Moore GE 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》2006,20(2):422-434
The purpose of this report is to offer a consensus opinion of ACVIM diplomates on the diagnosis, treatment, and prevention of Borrelia burgdorferi infections in dogs (canine Lyme disease). Clinical syndromes known to commonly be associated with canine Lyme disease include polyarthritis and glomerulopathy. Serological test results can be used to document exposure to B. burgdorferi but not prove illness. Although serum enzyme-linked immunosorbent assay/indirect fluorescent antibody assay titers can stay positive for months to years after treatment, quantitative C6 peptide antibody paired tests need more study. Serological screening of healthy dogs is controversial because it can lead to overdiagnosis or overtreatment of normal dogs, most of which never develop Lyme disease. However, serological screening can provide seroprevalence and sentinel data and stimulate owner education about tick infections and control. Although it is unknown whether treatment of seropositive healthy dogs is beneficial, the consensus is that seropositive dogs should be evaluated for proteinuria and other coinfections and tick control prescribed. Tick control can include a product that repels or protects against tick attachment, thereby helping to prevent transmission of coinfections as well as Borrelia spp. Seropositive dogs with clinical abnormalities thought to arise from Lyme disease generally are treated with doxycycline (10 mg/kg q24h for 1 month). Proteinuric dogs might need longer treatment as well as medications and diets for protein-losing nephropathy. The ACVIM diplomates believe the use of Lyme vaccines still is controversial and most do not administer them. It is the consensus opinion that additional research is needed to study predictors of illness, "Lyme nephropathy," and coinfections in Lyme endemic areas. 相似文献
994.
Peek SF Semrad S McGuirk SM Riseberg A Slack JA Marques F Coombs D Lien L Keuler N Darien BJ 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》2006,20(3):569-574
This prospective study compared survival rates of critically ill and septic foals receiving 1 of 2 different types of commercial equine plasma and analyzed admission variables as possible predictors of survival. Standardized clinical, hematologic, biochemical, and hemostatic admission data were collected and foals received either conventional commercially available hyperimmune equine plasma or equine plasma specifically rich in antiendotoxin antibodies in a double-blinded, coded fashion. Sepsis was defined as true bacteremia or sepsis score >11. Overall survival rate to discharge was 72% (49/68). Foals that were nonbacteremic and demonstrated a sepsis score of < or = 11 at admission had a 95% (18/19) survival rate. The survival rate to discharge for septic foals was 28/49 (57%), with truly bacteremic foals having a survival rate of 58% (14/24), whereas that for nonbacteremic, septic foals was 56% (14/25). Sensitivity and specificity for sepsis score >11 as a predictor of bacteremia were 74 and 52%, respectively. For the entire study population, a higher survival rate to discharge was documented for those foals receiving hyperimmune plasma rich in antiendotoxin antibodies (P = .012, odds ratio [OR] 6.763, 95% confidence interval [CI]: 1.311, 34.903). Administration of plasma rich in antiendotoxin antibodies also was associated with greater survival in septic foals (P = .019, OR 6.267, 95% CI: 1.186, 33.109). Statistical analyses demonstrated that, among 53 clinical and clinicopathologic admission variables, high sepsis score (P < .001), low measured IgG concentration (P = .01), high fibrinogen concentration (P = .018), low segmented neutrophil count (P = .028), and low total red blood cell numbers (P = .048) were the most significant predictors of overall mortality. 相似文献
995.
Sila DN Doungla E Smout C Van Loey A Hendrickx M 《Journal of agricultural and food chemistry》2006,54(22):8471-8479
In situ changes in pectin fractions for thermally processed carrots were related to textural changes. The texture of pretreated and subsequently thermally processed carrot disks was determined. Alcohol insoluble residue (AIR) was extracted from the pretreated and thermally processed tissues. The AIR was characterized in terms of the degree of methylation (DM) and changes in pectin fractions. Distinct differences in texture and DM were observed during thermal processing. Pretreatment conditions that induced a significant decrease in DM showed better textures. Demethoxylation caused interconversion of pectin fractions, water soluble pectin (WSP) changing into water insoluble pectin [chelator (CSP) and alkali (NSP) soluble pectin]. This process was reversed during cooking accompanied by remarkable alterations in molecular weight (MW) distribution patterns. The WSP depicted polydisperse MW distribution patterns, strongly dependent on the pretreatment condition. Confirmatory results of interconversions of pectin fractions (WSP, NSP) were demonstrated by the MW distribution patterns and neutral sugar profiles. All thermal related transformations of pectin structural parameters were decelerated by lowering the DM. 相似文献
996.
997.
998.
999.
Goll MG Kirpekar F Maggert KA Yoder JA Hsieh CL Zhang X Golic KG Jacobsen SE Bestor TH 《Science (New York, N.Y.)》2006,311(5759):395-398
The sequence and the structure of DNA methyltransferase-2 (Dnmt2) bear close affinities to authentic DNA cytosine methyltransferases. A combined genetic and biochemical approach revealed that human DNMT2 did not methylate DNA but instead methylated a small RNA; mass spectrometry showed that this RNA is aspartic acid transfer RNA (tRNA(Asp)) and that DNMT2 specifically methylated cytosine 38 in the anticodon loop. The function of DNMT2 is highly conserved, and human DNMT2 protein restored methylation in vitro to tRNA(Asp) from Dnmt2-deficient strains of mouse, Arabidopsis thaliana, and Drosophila melanogaster in a manner that was dependent on preexisting patterns of modified nucleosides. Indirect sequence recognition is also a feature of eukaryotic DNA methyltransferases, which may have arisen from a Dnmt2-like RNA methyltransferase. 相似文献
1000.
An enigmatic stepwise increase in oxygen in the late Precambrian is widely considered a prerequisite for the expansion of animal life. Accumulation of oxygen requires organic matter burial in sediments, which is largely controlled by the sheltering or preservational effects of detrital clay minerals in modern marine continental margin depocenters. Here, we show mineralogical and geochemical evidence for an increase in clay mineral deposition in the Neoproterozoic that immediately predated the first metazoans. Today most clay minerals originate in biologically active soils, so initial expansion of a primitive land biota would greatly enhance production of pedogenic clay minerals (the "clay mineral factory"), leading to increased marine burial of organic carbon via mineral surface preservation. 相似文献