全文获取类型
收费全文 | 3968篇 |
免费 | 279篇 |
国内免费 | 148篇 |
专业分类
林业 | 374篇 |
农学 | 317篇 |
基础科学 | 104篇 |
831篇 | |
综合类 | 641篇 |
农作物 | 241篇 |
水产渔业 | 401篇 |
畜牧兽医 | 968篇 |
园艺 | 164篇 |
植物保护 | 354篇 |
出版年
2024年 | 9篇 |
2023年 | 46篇 |
2022年 | 84篇 |
2021年 | 159篇 |
2020年 | 173篇 |
2019年 | 160篇 |
2018年 | 161篇 |
2017年 | 161篇 |
2016年 | 162篇 |
2015年 | 152篇 |
2014年 | 189篇 |
2013年 | 210篇 |
2012年 | 328篇 |
2011年 | 351篇 |
2010年 | 185篇 |
2009年 | 202篇 |
2008年 | 242篇 |
2007年 | 256篇 |
2006年 | 199篇 |
2005年 | 162篇 |
2004年 | 107篇 |
2003年 | 101篇 |
2002年 | 101篇 |
2001年 | 75篇 |
2000年 | 56篇 |
1999年 | 76篇 |
1998年 | 40篇 |
1997年 | 31篇 |
1996年 | 31篇 |
1995年 | 28篇 |
1994年 | 34篇 |
1993年 | 27篇 |
1992年 | 23篇 |
1991年 | 10篇 |
1990年 | 12篇 |
1989年 | 11篇 |
1988年 | 10篇 |
1987年 | 8篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1977年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1967年 | 1篇 |
1965年 | 1篇 |
1955年 | 1篇 |
1943年 | 1篇 |
1940年 | 1篇 |
排序方式: 共有4395条查询结果,搜索用时 125 毫秒
991.
Gómez-Ochoa P Miana-Mena FJ Muñoz MJ Cativiela E Gómez F 《Research in veterinary science》2006,81(1):87-91
The aim of this work was to isolate and cultivate a subpopulation of pluripotent stem cells present in peripheral blood of different animal species, frequently used in laboratory studies (mice, rats and hamsters). Pluripotent stem cells (PSCs), already described in human beings, are fibroblast-like cells that exhibit a CD34 marker, specific for haematopoietic stem cells. Commonly used human commercial media were investigated for culturing animal PSCs. These findings suggest that this simple and standardized methodology may be applicable in several fields such as the study of the pharmacological effects of drugs on the haematopoietic line and the study of new strategies in cellular therapy for some human diseases. 相似文献
992.
Negrão MR Keating E Faria A Azevedo I Martins MJ 《Journal of agricultural and food chemistry》2006,54(14):4982-4988
Alkaline phosphatase (ALP) is an ecto-enzyme widely distributed across species. It modulates a series of transmembranar transport systems, has an important role in bone mineralization, and can also be involved in vascular calcification. Polyphenol-rich diets seem to have protective effects on human health, namely, in the prevention of cardiovascular diseases. We aimed to investigate the effects of polyphenols and polyphenol-rich beverages upon membranar alkaline phosphatase (ecto-ALP) activity in intact human vascular smooth muscle cells (AALTR). The ecto-ALP activity was determined at pH 7.8, with p-nitrophenyl phosphate as the substrate, by absorbance spectrophotometry at 410 nm. Cell viability was assessed by the lactate dehydrogenase (LDH) method, and the polyphenol content of beverages was assessed using the Folin-Ciocalteu reagent. All polyphenols tested inhibited ecto-ALP activity, in a concentration-dependent way. Teas, wines, and beers also inhibited ecto-ALP activity, largely according to their polyphenol content. All tested compounds and beverages improved or did not change AALTR cell viability. Stout beer was an exception to the described behavior. Although more studies must be done, the inhibition of AALTR ecto-ALP activity by polyphenolic compounds and polyphenol-containing beverages may contribute to their cardiovascular protective effects. 相似文献
993.
García-Marco S Torreblanca A Lucena JJ 《Journal of agricultural and food chemistry》2006,54(4):1380-1386
EDDHA/Fe3+ chelates are the most common fertilizers used to solve Fe chlorosis in established crops. Commercial products contain two regioisomers, ethylenediamine-N,N'-bis(o-hydroxyphenylacetic) acid (o,o-EDDHA)/Fe3+ and ethylenediamine-N-(o-hydroxyphenylacetic)-N'-(p-hydroxyphenylacetic) acid (o,p-EDDHA)/Fe3+. Although several chromatographic methods exist for the determination of Fe3+ chelated by the o,o-EDDHA isomer, no method has been described for the quantification of Fe3+ chelated by o,p-EDDHA. In this work, factors that affect the behavior of o,p-EDDHA/Fe3+ in ion pair chromatography are reviewed: pH, ion pair reagent, and organic modifier. The best chromatographic performance was obtained with an aqueous mobile phase at pH 6.0 containing 35% acetonitrile and 5 mM tetrabutylammonium hydroxide under isocratic elution conditions. This method was applied to the quantification of commercial samples. 相似文献
994.
A new procedure to determine individual sugar (sucrose, glucose, and fructose) 13C isotope ratios, using liquid chromatography-isotope ratio mass spectrometry (HPLC-IRMS), has been developed to improve isotopic methods devoted to the study of honey authenticity. For this purpose 79 commercial honey samples from various origins were analyzed. Values of delta13Choney ranged from -14.2 to -27.2", and delta13Cprotein ranged from -23.6 to -26.9". A very strong correlation is observed between the individual sugar 13C ratios, which are altered in the event of sugar addition, even at low levels. The use of Deltadelta13C [fruct-glu], Deltadelta13C [fruct-suc], and Deltadelta13C [gluc-suc] systematic differences as an authenticity criterion permits the sugar addition [C3, beet sugar; or C4, cane sugar, cane syrup, isoglucose syrup, and high-fructose corn syrup (HFCS)] to be reliably detected (DL = 1-10%). The new procedure has advantages over existing methods in terms of analysis time and sensitivity. In addition, it is the first isotopic method developed that allows beet sugar addition detection. 相似文献
995.
Amenomori M Ayabe S Bi XJ Chen D Cui SW Danzengluobu Ding LK Ding XH Feng CF Feng Z Feng ZY Gao XY Geng QX Guo HW He HH He M Hibino K Hotta N Hu H Hu HB Huang J Huang Q Jia HY Kajino F Kasahara K Katayose Y Kato C Kawata K Labaciren Le GM Li AF Li JY Lou YQ Lu H Lu SL Meng XR Mizutani K Mu J Munakata K Nagai A Nanjo H Nishizawa M Ohnishi M Ohta I Onuma H Ouchi T Ozawa S Ren JR Saito T Saito TY Sakata M Sako TK Sasaki T Shibata M Shiomi A Shirai T Sugimoto H Takita M Tan YH Tateyama N Torii S 《Science (New York, N.Y.)》2006,314(5798):439-443
The intensity of Galactic cosmic rays is nearly isotropic because of the influence of magnetic fields in the Milky Way. Here, we present two-dimensional high-precision anisotropy measurement for energies from a few to several hundred teraelectronvolts (TeV), using the large data sample of the Tibet Air Shower Arrays. Besides revealing finer details of the known anisotropies, a new component of Galactic cosmic ray anisotropy in sidereal time is uncovered around the Cygnus region direction. For cosmic-ray energies up to a few hundred TeV, all components of anisotropies fade away, showing a corotation of Galactic cosmic rays with the local Galactic magnetic environment. These results have broad implications for a comprehensive understanding of cosmic rays, supernovae, magnetic fields, and heliospheric and Galactic dynamic environments. 相似文献
996.
Trapp SM Dagnone AS Vidotto O Freire RL Amude AM de Morais HS 《Veterinary parasitology》2006,140(3-4):223-230
Canine ehrlichiosis and babesiosis have a worldwide distribution with geographic variation in prevalence and main clinical manifestations. We prospectively determined seroprevalence of canine babesiosis and ehrlichiosis, and risk factors for seropositivity. Three hundred and eighty-one dogs were randomly selected to represent the canine population at a Veterinary Teaching Hospital in south Brazil (latitude 23° S). Dogs were tested with a point-of-care ELISA for Ehrlichia canis antibodies and IFA to confirm previous exposure to Babesia vogeli. Multiple logistic regression analysis was then used to estimate adjusted odds ratio (OR) and their 95% confidence intervals. One hundred and thirty-six (36%) dogs were seropositive for B. vogeli antibodies, whereas 87 (23%) dogs were seropositive to E. canis antibodies. Fifty-four (14%) dogs seroreacted to both agents. Adult dogs previously infested with ticks were more likely to seroreact to B. vogeli or E. canis. Superficial bleeding (OR = 12.4) was more common in dogs exposed to B. vogeli, whereas neurological signs (OR = 7.7) were more common in dogs seropositive to E. canis. Neurological signs (OR = 12.0) and lameness (OR = 12.8) were more prevalent in dogs that seroreacted to both organisms. Owners of dogs with ticks were more likely to have been exposed to ticks themselves (OR = 3.2). Canine babesiosis and ehrlichiosis appear to be highly prevalent in this hospital population. Clinical signs differed from the most common signs in other regions with bleeding occurring more in dogs seropositive to babesiosis, but not ehrlichiosis; neurologic signs in dogs with E. canis antibodies; and lameness in dogs that seroreacted to both organisms. 相似文献
997.
辽宁绒山羊改良当地蒙藏山羊试验效果观察 总被引:1,自引:1,他引:0
用辽宁绒山羊改良引进的内蒙古白绒山羊与甘南当地藏山羊,结果表明:辽蒙藏杂交F1代绒山羊,在初生、3月龄、6月龄、12月龄各个时期,其体重、体高、体长、胸围与对照组(蒙藏山羊杂交后代)相比,公羊除初生和3月龄羔羊的体长、12月龄胸围差异不显著外(P〉0.05),其它均极显著的高于对照组;母羊的3月龄、12月龄体重与对照组差异极显著(P〈0.01),初生、6月龄体重差异显著(0.01〈P〈0.05),初生、3月龄、6月龄体高、胸围及6月龄体长与对照组差异极显著(P〈0.01),公、母羊绒细度、长度、单纤维断裂强力、单纤维断裂伸长率等指标差异不显著(P〉0.05),含绒率和产绒量差异极显著(P〈0.01)。杂交F1代羊杂交优势明显,效果显著。 相似文献
998.
Carmen Sotelo Montes John C. Weber Dimas A. Silva Clarice Andrade Graciela I. B. Mu?iz Rosilei A. Garcia Antoine Kalinganire 《Annals of Forest Science》2012,69(6):747-756
? Context
There is little information about inter- and intra-specific variation in fuelwood properties of trees/shrubs in West Africa.? Aims
We studied variation in fuelwood properties of Balanites aegyptiaca, Combretum glutinosum, Guiera senegalensis, Piliostigma reticulatum, and Zizyphus mauritiana in the Sahelian and Sudanian ecozones of Mali.? Methods
Trees were sampled on different soil (sandy, sandy/loam, or rocky), land use (parkland agroforest or woodland), and terrain (flat, temporarily flooded, or hill slope) types in five regions extending from the drier eastern to the more humid western parts of Mali. Basic density, volatile matter, fixed carbon, ash content, moisture content, gross calorific value, and fuel value index were measured for each tree and adjusted for tree age.? Results
All fuelwood properties differed significantly among species, but there were significant species by region interactions. Most fuelwood properties of four species differed significantly among regions. Soil and/or land use type had significant effects on a few fuelwood properties of four species.? Conclusion
In general, fuelwood production is recommended in all regions for G. senegalensis, in drier regions for B. aegyptiaca and C. glutinosum, in more humid regions for Z. mauritiana, and on rocky soils for all species. Fuelwood production of P. reticulatum is not recommended. 相似文献999.
1000.
SB Grant JD Saphores DL Feldman AJ Hamilton TD Fletcher PL Cook M Stewardson BF Sanders LA Levin RF Ambrose A Deletic R Brown SC Jiang D Rosso WJ Cooper I Marusic 《Science (New York, N.Y.)》2012,337(6095):681-686
Humans create vast quantities of wastewater through inefficiencies and poor management of water systems. The wasting of water poses sustainability challenges, depletes energy reserves, and undermines human water security and ecosystem health. Here we review emerging approaches for reusing wastewater and minimizing its generation. These complementary options make the most of scarce freshwater resources, serve the varying water needs of both developed and developing countries, and confer a variety of environmental benefits. Their widespread adoption will require changing how freshwater is sourced, used, managed, and priced. 相似文献