全文获取类型
收费全文 | 140590篇 |
免费 | 7036篇 |
国内免费 | 95篇 |
专业分类
林业 | 7099篇 |
农学 | 4678篇 |
基础科学 | 848篇 |
16163篇 | |
综合类 | 24752篇 |
农作物 | 5725篇 |
水产渔业 | 6827篇 |
畜牧兽医 | 70763篇 |
园艺 | 1863篇 |
植物保护 | 9003篇 |
出版年
2018年 | 1857篇 |
2017年 | 2034篇 |
2016年 | 1879篇 |
2015年 | 1747篇 |
2014年 | 2077篇 |
2013年 | 4950篇 |
2012年 | 3780篇 |
2011年 | 4380篇 |
2010年 | 2902篇 |
2009年 | 2842篇 |
2008年 | 4278篇 |
2007年 | 4066篇 |
2006年 | 3873篇 |
2005年 | 4289篇 |
2004年 | 4198篇 |
2003年 | 4019篇 |
2002年 | 3478篇 |
2001年 | 4200篇 |
2000年 | 4170篇 |
1999年 | 3469篇 |
1998年 | 1471篇 |
1997年 | 1403篇 |
1995年 | 1517篇 |
1994年 | 1355篇 |
1993年 | 1347篇 |
1992年 | 2800篇 |
1991年 | 2913篇 |
1990年 | 3092篇 |
1989年 | 2918篇 |
1988年 | 2764篇 |
1987年 | 2638篇 |
1986年 | 2742篇 |
1985年 | 2670篇 |
1984年 | 2216篇 |
1983年 | 2001篇 |
1982年 | 1294篇 |
1979年 | 2153篇 |
1978年 | 1687篇 |
1977年 | 1489篇 |
1976年 | 1410篇 |
1975年 | 1584篇 |
1974年 | 1882篇 |
1973年 | 1950篇 |
1972年 | 1945篇 |
1971年 | 1839篇 |
1970年 | 1731篇 |
1969年 | 1693篇 |
1968年 | 1415篇 |
1967年 | 1520篇 |
1966年 | 1410篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
de Laforcade AM Freeman LM Shaw SP Brooks MB Rozanski EA Rush JE 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》2003,17(5):674-679
Sepsis is a frequent source of morbidity and mortality in critically ill patients. The goal of this case control study was to measure hemostatic changes in dogs with naturally occurring sepsis. Blood was collected within 24 hours of admission from 20 dogs that fulfilled the criteria for sepsis. Sepsis was defined as histologic or microbiological confirmation of infection and 2 or more of the following criteria: hypo- or hyperthermia, tachycardia, tachypnea, or leukopenia, leukocytosis, or > 3% bands. Culture and sensitivities were performed on appropriate samples from all septic dogs. Twenty-eight control dogs were enrolled on the basis of normal results of physical examination, CBC, serum biochemistry, and coagulation profile. Plasma samples were analyzed for prothrombin time (PT), partial thromboplastin time (PTT), fibrin(ogen) degradation products (FDP), D-dimer (DD) concentrations, antithrombin (AT) activity, and protein C (PC) activity. Data were compared between groups by chi-square or independent t-tests. PC (P < .001) and AT (P < .001) activities were significantly lower in dogs with sepsis compared to controls. Dogs with sepsis had significantly higher PT (P = .007), PTT (P = .005), D-dimer (P = .005), and FDP (P = .001) compared to controls. Platelet counts were not significantly different between groups. Ten of the 20 septic dogs (50%) died, but no association was identified between any of the measured variables and outcome. These findings are consistent with previous studies in animals with experimentally induced disease and in clinical studies of humans. On the basis of these results, further investigation of the role of AT and PC in canine sepsis is warranted. 相似文献
992.
İsmail Hakkı Nur William Pérez Horst Erich König 《Anatomia, histologia, embryologia》2021,50(3):658-667
This study aims to reveal the morphological properties of facial nerve and the middle ear in Van cats. Study material was composed of 6 female Van cats. Dissections were performed under a Zoom Stereo Microscope. There was no plexus buccalis in Van cats. The chorda tympani was observed to pass through an opening in the tympanic cavity, emerge through a small opening just behind the retroarticular process, and join the lingual nerve. A rounded anatomical formation with a size of 2.75 ± 0.3 mm was found to be located within the mastoid process of the temporal bone between the facial nerve and the auricular branch of the vagus nerve. The stapes nerve was not present. The geniculate ganglion was very prominent and about 1.00 mm high. The deep petrosal nerve was observed to emerge from the plexus tympanicus. The bulla tympanica was 18.96 ± 0.10 mm long, 13.03 ± 0.20 mm wide and 13.16 ± 0.20 mm high. After leaving the mandibular nerve, the n.tensoris tympani coursed caudally around the a.maxillaris, formed an ansa, entered the tympanic cavity through the canalis musculotubarius and reached an end in the m. tensor tympani. Due to the scarcity of studies on the middle ears of Van cats, it is thought that this study will fill a gap in the field of veterinary anatomy. 相似文献
993.
994.
995.
J.W. Lehmkuhler E.E.D. Felton D.A. Schmidt K.J. Bader H.E. Garrett M.S. Kerley 《Agroforestry Systems》2003,59(1):35-42
Silvopastoral systems offer an alternative to the conventional cow-calf segment of the beef industry in the Midwestern region
of the United States. Little information exists for transitioning from a conventional pasture-based beef operation to a silvopastoral
system utilizing multiple deciduous tree species. Nine pastures approximately 1 ha in size were established with a mixture
of cool-season grasses and legumes to investigate tree protection methods and cattle performance. Four tree species (Juglans nigra, Gleditsia triacanthos, Quercus rubra, & Carya illinoensis) were planted within six of these pastures. Three methods of protection were tested, and included a no protection control
(Con), foliar application of 0.20% denatonium benzoate (TreeGuard™), or a single strand of electrified poly-wire (EF) in each
of the two grazing years. Cattle damage to young trees was prominent during the two years for Con and TreeGuard™. EF offered
acceptable protection. Red oak trees suffered the highest degree of damage from livestock. Establishing trees within grazed
pastures did not hinder performance of beef cattle. Transitioning from conventional pastures to silvopastures can be accelerated
utilizing an electrified fencing system to prevent cattle damage.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
996.
Johansson L Rytkonen A Bergman P Albiger B Källström H Hökfelt T Agerberth B Cattaneo R Jonsson AB 《Science (New York, N.Y.)》2003,301(5631):373-375
The human-specific bacterial pathogen Neisseria meningitidis is a major cause of sepsis and/or meningitis. The pili of N. meningitidis interact with CD46, a human cell-surface protein involved in regulation of complement activation. Transgenic mice expressing human CD46 were susceptible to meningococcal disease, because bacteria crossed the blood-brain barrier in these mice. Development of disease was more efficient with piliated bacteria after intranasal, but not intraperitoneal, challenge of CD46 transgenic mice, suggesting that human CD46 facilitates pilus-dependent interactions at the epithelial mucosa. Hence, the human CD46 transgenic mice model is a potentially useful tool for studying pathogenesis and for vaccine development against meningococcal disease. 相似文献
997.
998.
Generalized marker regression and interval QTL mapping methods for binary traits in half-sib family designs 总被引:3,自引:0,他引:3
H. N. Kadarmideen & J. C. M. Dekkers 《Zeitschrift für Tierzüchtung und Züchtungsbiologie》2001,118(5):297-309
A Generalized Marker Regression Mapping (GMR) approach was developed for mapping Quantitative Trait Loci (QTL) affecting binary polygenic traits in a single-family half-sib design. The GMR is based on threshold-liability model theory and regression of offspring phenotype on expected marker genotypes at flanking marker loci. Using simulation, statistical power and bias of QTL mapping for binary traits by GMR was compared with full QTL interval mapping based on a threshold model (GIM) and with a linear marker regression mapping method (LMR). Empirical significance threshold values, power and estimates of QTL location and effect were identical for GIM and GMR when QTL mapping was restricted to within the marker interval. These results show that the theory of the marker regression method for QTL mapping is also applicable to binary traits and possibly for traits with other non-normal distributions. The linear and threshold models based on marker regression (LMR and GMR) also resulted in similar estimates and power for large progeny group sizes, indicating that LMR can be used for binary data for balanced designs with large families, as this method is computationally simpler than GMR. GMR may have a greater potential than LMR for QTL mapping for binary traits in complex situations such as QTL mapping with complex pedigrees, random models and models with interactions. 相似文献
999.
P.S. Mir K.S. Schwartzkopf-Genswein T. Entz K.K. Klein E. Okine M.V. Dodson 《Livestock Science》2008,116(1-3):22-29
The effect of feed withdrawal for 48 h, prior to initiation of the finishing (fattening) period (75 d) on carcass marbling fat was studied in 120 European × British cross-bred heifers with an average weight of 585 ± 39 kg. Heifers were randomized in a 2 × 2 factorial design experiment with two dietary management treatments, where half the heifers were provided the feed components of steam rolled barley and barley silage either free choice or as a total mixed ration (TMR) containing 87% steam rolled barley and 13% barley silage with ad libitum vitamins and minerals via salt blocks for all animals. Within each dietary management treatment, 30 heifers were denied feed (water was available) for 48 h prior to the two week adaptation to the high grain diet preceding the 75 d finishing period. At the end of the 48 h feed denial blood samples were collected from the jugular vein prior to feeding for determination of glucose and insulin concentrations, which indicated that 48 h feed withdrawal consistently decreased (P = 0.0001) plasma concentrations of both glucose and insulin but the ratios of the concentrations of glucose to insulin were not affected. At slaughter samples of subcutaneous fat from the brisket (BF) and skirt muscle (pars costalis diaphragmatis; PCD) were procured for determination of chemical fat content, fat dissected from the muscle and for enumeration of adipocytes, less than 35 μm in diameter and to determine the average cell size in the dissected fat and from the BF by flow-cytometry of adipocytes fixed in osmium tetroxide. The carcass characteristics were also obtained. Although no differences due feed withdrawal for 48 h were evident for carcass weight, percent lean (saleable) meat yield, rib eye area, average fat cover, fat content of PCD or BF, the US marbling score was increased (P = 0.048) and the amount of dissected fat from the muscle tended to be higher (P = 0.107), thus 81% of the carcasses graded “US Choice” or “Canada AAA,” or displayed at least a “small” amount of intramuscular fat as compared (P = 0.0807) to 68% of the heifers not denied feed. Based on more than three years of weekly prices of carcasses that graded “Canada AAA” and “Canada AA,” these experimental results suggested that the expected price of a finished heifer could increase by $4.61 Canadian if a 48 h feed withdrawal was imposed prior to initiation of the finishing phase. Although significant differences in adipocyte numbers due to a single time 48 h feed withdrawal prior to initiation of the finishing phase were not detected, the carcass quality factors were affected leading to an odds ratio of 1.84 times in favour of cattle carcasses to grade “Canada AAA” than if fed continuously. 相似文献
1000.
Polarised light biomicroscopy was used to examine the normal pre-corneal tear film in 21 eyes of 12 pekingese dogs. The purpose of the study was to examine the influence of excessive exophthalmos on the pre-corneal tear film in the dog. The majority of the animals were found to have high levels of ocular surface contamination by particulate material and plaques of viscous mucus. Other abnormalities included surface lipid with an abnormal granular (three dogs) or 'curdled' (two dogs) appearance; excessive thinning of the lipid layer of the tear film; and the presence of dark globular structures in two dogs, which were presumed to be abnormal meibomian lipid. Break up of the tear film was observed in one dog. Grossly, a thread of viscous mucus was frequently observed along the margin of the lower eyelid. It is postulated that this thread forms because of the excessively exophthalmic conformation of the breed, which prevents the normal access of effete mucus and entrapped debris to the lower conjunctival fornix. The combination of the above factors in the pekingese is suggested as the mechanism whereby the tear film has a reduced stability, thus enhancing the risk from factors more usually considered to initiate corneal ulceration in the breed. The possible adverse effects of lid splitting for the mass removal of distichiae in exophthalmic dogs is discussed. 相似文献