全文获取类型
收费全文 | 45589篇 |
免费 | 2126篇 |
国内免费 | 25篇 |
专业分类
林业 | 1852篇 |
农学 | 1410篇 |
基础科学 | 283篇 |
6619篇 | |
综合类 | 6374篇 |
农作物 | 1967篇 |
水产渔业 | 2036篇 |
畜牧兽医 | 24070篇 |
园艺 | 522篇 |
植物保护 | 2607篇 |
出版年
2020年 | 389篇 |
2019年 | 474篇 |
2018年 | 857篇 |
2017年 | 962篇 |
2016年 | 775篇 |
2015年 | 536篇 |
2014年 | 827篇 |
2013年 | 2242篇 |
2012年 | 1292篇 |
2011年 | 1650篇 |
2010年 | 1151篇 |
2009年 | 1115篇 |
2008年 | 1606篇 |
2007年 | 1524篇 |
2006年 | 1341篇 |
2005年 | 1132篇 |
2004年 | 1093篇 |
2003年 | 1058篇 |
2002年 | 927篇 |
2001年 | 1181篇 |
2000年 | 1170篇 |
1999年 | 890篇 |
1998年 | 410篇 |
1997年 | 417篇 |
1995年 | 451篇 |
1993年 | 365篇 |
1992年 | 650篇 |
1991年 | 708篇 |
1990年 | 715篇 |
1989年 | 735篇 |
1988年 | 618篇 |
1987年 | 585篇 |
1986年 | 666篇 |
1985年 | 581篇 |
1984年 | 525篇 |
1983年 | 493篇 |
1979年 | 714篇 |
1978年 | 479篇 |
1977年 | 512篇 |
1976年 | 603篇 |
1975年 | 649篇 |
1974年 | 738篇 |
1973年 | 680篇 |
1972年 | 676篇 |
1971年 | 571篇 |
1970年 | 566篇 |
1969年 | 615篇 |
1968年 | 589篇 |
1967年 | 593篇 |
1966年 | 586篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
53.
Ovine-derived fibroblasts were used to validate an insulin-like growth factor I (IGF-I) membrane-receptor binding assay system. Competitive binding using fibroblasts revealed that half-maximal inhibition of 125I-IGF-I binding by IGF-I was 2.3 nM. SDS-polyacrylamide gel electrophoresis analysis of specific protein-associated 125I-IGF-I was consistent with the migration of 125I-IGF-I-labeled Type I IGF receptor alpha-subunits at Mr 133,000 daltons. Further, the efficiency of two cell solubilization methods was examined and time-dependent binding equilibrium was determined for the membrane assay system. Satellite cell-derived myotubes were subsequently isolated from primary satellite cell cultures established from the semimembranosus muscles of high and low efficiency-of-gain (EOG) Targhee rams, and IGF-I receptor dynamics were measured. A membrane competitive binding study revealed that half-maximal inhibition of 125I-IGF-I binding was achieved by 1-ng IGF-I for low, and 10-ng IGF-I for high, EOG myotube membrane preparations. Kd values were similar between the high EOG (4.78 nM) and low EOG (2.95 nM) groups; however, receptor concentrations (Bmax) appeared to differ between groups. High EOG membrane receptor Bmax was 3.88 pmole/micrograms protein (19.87 pmole/micrograms DNA), whereas low EOG membrane receptor Bmax was 1.22 pmole/micrograms protein (9.28 pmole/micrograms DNA). These preliminary findings support the hypothesis that genetic selection for EOG results in altered satellite cell responsiveness to IGF-I. 相似文献
54.
55.
Hypothalamic neurotransmitter concentrations and meat quality in stressed pigs offered excess dietary tryptophan and tyrosine. 总被引:2,自引:0,他引:2
Pale, soft, exudative (PSE) pork occurs, for the most part, from environmental stress on the pig. Amino acid intake may be related to stress susceptibility through hormone and neurotransmitter induction. Two experiments were conducted to determine whether supplementation of 5 g of tryptophan (TRP) or 10 g of tyrosine (TYR) per kilogram of a 14% CP diet would alter the response of pigs to stress as measured by hypothalamic neurotransmitter concentrations and incidence of PSE. Twenty-four (Exp. 1) and 36 (Exp. 2) 92-kg pigs were offered one of three diets: control, TRP-, or TYR-supplemented for 5 d before slaughter. Dietary TRP or TYR supplementation in Exp. 1. doubled (P less than .05) plasma TRP and TYR concentrations, respectively, and increased (P less than .05) 5-hydroxytryptamine, dihydroxyphenyl ethylamine, dihydroxyphenyl acetic acid, and homovanillic acid concentrations in the hypothalamus. Pigs that exhibited stress at slaughter had lower (P less than .05) hypothalamic concentrations of epinephrine, norepinephrine, and 5-hydroxytryptamine. In Exp. 2, pigs were trucked 55 km to a commercial meat packing facility and slaughtered without a rest period. This handling procedure was designed to invoke a high incidence of PSE pork and thus be a strong test of treatments. Supplemental dietary amino acids seemed to alter the frequency distribution of the severity of PSE pork. These data indicate that dietary manipulation of amino acid precursors of neurotransmitters may offer a practical means of reducing stress response in swine. 相似文献
56.
57.
P O Ahmed M F Miller S D Shackelford L P Johnson S E Williams M A McCann J O Reagan 《Journal of animal science》1992,70(2):439-443
Thirty-two crossbred cattle (steers = 17; heifers = 15) exhibiting an ultrasound fat thickness at the 12 to 13th rib region of at least 10 mm were selected from a slaughter shift at a commercial packing plant. After splitting, alternating sides of each carcass were trimmed of 1) subcutaneous fat in excess of 6.4 mm; 2) all kidney, pelvic, and heart fat; and 3) all cod or udder fat and fat in the flank region. Both sides of each carcass were fabricated into subprimals (final trim level of 6.4 mm) according to normal industry procedures. Effect of hot-fat trimming, yield grade (3, 4, and 5), and gender on hot-fat trim, fabrication fat trim, major subprimal, and total subprimal yield of untrimmed and trimmed carcasses were determined. Higher numerical yield grade (YG) corresponded with higher (P less than .05) percentages of hot-fat trim. Hot-fat trimming increased (P less than .05) the difference in fabrication fat trim between steers and heifers and between YG 3 and YG 5. Steers and heifers differed (P less than .05) in percentage of major subprimals and total subprimals when processed conventionally, whereas hot-fat trimming eliminated this difference (P less than .05). Untrimmed YG 3 carcasses had 3.1 and 5.0% higher major subprimal yield (P less than .05) than untrimmed YG 4 and YG 5 carcasses, respectively, whereas hot-fat trimming reduced this difference to 2.5% for YG 4 and to 3.7% for YG 5.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
58.
Matthew A.O. Atilola DVM PhD Joanne R. Cockshutt DVM MS Ron Mclaughlin DVM DVSc Susan M. Cochrane DVM DVSc Paul W. Pennock DVM MS 《Veterinary radiology & ultrasound》1993,34(5):321-324
Five clinically normal five year old dogs were used in this study. From a randomised table inter ver tebral discs were each injected with either collagenase or calcium chloride diluent. The surgically exposed cervical discs were injected with 50 units whereas thoracic and lumbar discs were injected under fluoroscopic guidance with 100 units of the enzyme. Postinjection radiographs revealed significant (p ≤ .05) disc space narrowing in enzyme injected discs. The cervical discs had the highest frequency of radiographic narrowing (87%) followed by the thoracic (70%) and lumbar (53%) discs. Spondylosis deformans developed at the sites of cervical enzyme injections. None of the dogs had neurologic abnormalities one year postinjection. 相似文献
59.
In 5 herds in which bovine virus diarrhoea virus (BVDV) had been isolated, all animals were bled for virological and serological examination. After the herd blood test, follow up blood tests were made on calves born up to 6 months later in 1 herd, 9 months later in 1 herd and up to 12 months later in 3 herds. Persistently infected animals (PI animals) were removed and after a time period a small herd sample of 10 animals that were born after removal of the PI animals were examined for BVDV antibodies.At the herd blood test a total of 21 PI animals were detected. During the follow up period another 25 PI animals were born.Among animals in the small herd samples collected after removal of the PI animals, antibody positive animals were found in the 2 herds with the shortest follow up period. In the 3 herds with a 1 year follow up period there were no antibody carriers in the herd sample.It seems possible to prevent further spread of infection with BVDV if all animals in the herds as well as animals born during the following year are examined and PI animals removed. 相似文献
60.
Feline leukemia virus detection by immunohistochemistry and polymerase chain reaction in formalin-fixed, paraffin-embedded tumor tissue from cats with lymphosarcoma.
下载免费PDF全文
![点击此处可从《Canadian journal of veterinary research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
M L Jackson D M Haines S M Meric V Misra 《Canadian journal of veterinary research》1993,57(4):269-276
The prevalence of feline leukemia virus (FeLV) antigen and DNA was assessed in formalin-fixed, paraffin-embedded tumor tissues from 70 cats with lymphosarcoma (LSA). Tissue sections were tested for FeLV gp70 antigen using avidinbiotin complex (ABC) immunohistochemistry (IHC); DNA was extracted and purified from the same tissue blocks for polymerase chain reaction (PCR) amplification of a 166 base pair region of the FeLV long terminal repeat (LTR). Results were related to antemortem FeLV enzyme-linked immunosorbent assay (ELISA) for serum p27 antigen, anatomic site of LSA, and patient age. Viral DNA was detected by PCR in 80% of cases and viral antigen by IHC in 57% of cases. Seventeen cases were PCR-positive and IHC-negative; one case was PCR-negative and IHC-positive. Clinical records included FeLV ELISA results for 30 of 70 cats. All 19 ELISA-positive cats were positive by PCR and IHC; of the 11 ELISA-negative cats that were negative by IHC, seven were positive by PCR. When evaluated according to anatomic site, FeLV DNA and antigen were detected less frequently in intestinal LSAs than in multicentric and mediastinal tumors. Lymphosarcoma tissues from cats < 7 yr were several fold more likely to be positive for FeLV antigen by IHC than were tumors from cats > or = 7 yr. However, there was no significant difference in PCR detection of FeLV provirus between LSAs from cats < 7 yr and those > or = 7 yr.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献