全文获取类型
收费全文 | 14053篇 |
免费 | 1066篇 |
国内免费 | 72篇 |
专业分类
林业 | 626篇 |
农学 | 822篇 |
基础科学 | 125篇 |
2000篇 | |
综合类 | 1667篇 |
农作物 | 495篇 |
水产渔业 | 1042篇 |
畜牧兽医 | 7018篇 |
园艺 | 228篇 |
植物保护 | 1168篇 |
出版年
2023年 | 90篇 |
2021年 | 88篇 |
2020年 | 122篇 |
2019年 | 201篇 |
2018年 | 373篇 |
2017年 | 345篇 |
2016年 | 334篇 |
2015年 | 306篇 |
2014年 | 325篇 |
2013年 | 570篇 |
2012年 | 477篇 |
2011年 | 568篇 |
2010年 | 462篇 |
2009年 | 421篇 |
2008年 | 554篇 |
2007年 | 578篇 |
2006年 | 471篇 |
2005年 | 520篇 |
2004年 | 408篇 |
2003年 | 446篇 |
2002年 | 358篇 |
2001年 | 759篇 |
2000年 | 721篇 |
1999年 | 590篇 |
1998年 | 171篇 |
1997年 | 164篇 |
1996年 | 126篇 |
1995年 | 150篇 |
1994年 | 156篇 |
1993年 | 120篇 |
1992年 | 321篇 |
1991年 | 346篇 |
1990年 | 291篇 |
1989年 | 266篇 |
1988年 | 271篇 |
1987年 | 319篇 |
1986年 | 245篇 |
1985年 | 193篇 |
1984年 | 170篇 |
1983年 | 147篇 |
1982年 | 94篇 |
1981年 | 83篇 |
1980年 | 79篇 |
1979年 | 141篇 |
1978年 | 94篇 |
1977年 | 73篇 |
1975年 | 77篇 |
1974年 | 79篇 |
1971年 | 69篇 |
1969年 | 70篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Field experiments were conducted at Indian Agricultural Research Institute, New Delhi, during 2001–2002 and 2002–2003, to study the effect of inorganic, organic and Azotobacter combined sources of N on cotton (Gossypium hirsutum L.) and their residual effect on succeeding wheat (Triticum aestivum L.) crop. The results indicated considerable increase in yield attributes and mean seed cotton yield (2.33 Mg ha?1) with the combined application of 30 kg N and farmyard manure (FYM) at 12 Mg ha?1 along with Azotobacter (M4). The treatment in cotton that included FYM, especially when fertilizer N was also applied could either improve or maintain the soil fertility status in terms of available N, P and K. Distinct increase in yield attributes and grain yield of wheat was observed with the residual effect of integrated application of 30 kg N ha?1 + FYM at 12 Mg ha?1 + Azotobacter. Direct application of 120 kg N ha?1 resulted 67.4 and 17.7 % increase in mean grain yield of wheat over no N and 60 kg N ha?1, respectively. Integrated application of organic and inorganic fertilizer is therefore, recommended for higher productivity and sustainability of the cotton–wheat system. 相似文献
992.
J. Vilensky N. V. Koudinova A. Harmelin A. Scherz Y. Salomon 《Veterinary and comparative oncology》2005,3(4):182-193
Treatment of canine‐transmissible venereal tumour (CTVT) with local vascular‐targeted photodynamic therapy (VTP) using Pd‐bacteriopheophorbide (WST09) as a drug is suggested as an alternative to conventional chemotherapy. Male CD1 nude mice were subcutaneously grafted with the xenograft‐transmissible canine venereal tumour (XTVT). The VTP protocol delivered once consisted of intravenous administration of WST09 (10 mg kg?1) followed by immediate local illumination with a diode laser (763 nm). Controls included animals treated with light or WST09 alone. Macroscopic and microscopic evaluations of tumour response were conducted 10, 24 and 48 h after treatment. Upon VTP, tumours underwent necrosis that lasted 8–10 days and exhibited complete healing by 25–35 days, reaching an overall long‐term cure rate (83%) by 90 days after treatment. This study suggests that VTP with WST09 can efficiently treat CTVT in a single session, as compared with 4–6 sessions of chemotherapy and thus may be feasible for common veterinary practice, particularly under ambulatory conditions. 相似文献
993.
994.
A cellular association demarcated by two perpendiculars which were drawn between adjacent bundles of elongate spermatids from the tubular lumen to the basement membrane, was made the unit of histometrical observation in this study (provisionally called a “column”). Cell counting revealed that the average numbers per column of various types of germ cells do not show any significant differences among 5 fowls and between paired testes. The frequency of spermiogenic steps (numbered 1–8) was investigated in each column. A definite and common pattern was found in the frequency distribution in the 5 fowls observed. A relationship between spermiation and younger spermatid steps was also investigated in each column. The spermiation was found at different steps, but most frequently at step 2 (30.6 %). Based on these observations and referring to other author's information, an average time interval between two successive spermiations was calculated roughly at 3.3 ± 1.2 days. Theoretically, this value is equal to an average length of one epithelial cycle. Such a variable cycle may have caused irregular cellular associations in this species. 相似文献
995.
996.
M Funaba T Tanak M Kaneko T Iriki Y Hatano M Abe 《The Journal of veterinary medical science / the Japanese Society of Veterinary Science》2001,63(12):1355-1357
To compare the effects of two dietary protein sources, fish meal (FM) and corn gluten meal (CGM), fecal moisture content, nitrogen balance and urinary excretion were examined in adult cats. The dietary protein source did not cause a significant difference in daily food intake, water intake, urine volume, dry matter digestibility or urinary nitrogen excretion, but fecal moisture content was lower (P<0.02) in the CGM group. The HCl-insoluble fraction of urinary sediment tended to be higher in the CGM group (P<0.10), although urinary pH was similar in the two groups. These results suggest that CGM is comparable with FM in respect to nutritional value and the urine acidifying effect, but FM may be preferable to CGM for the prevention of constipation and struvite urolithiasis in cats. 相似文献
997.
This study was carried out to investigate the distribution of immune cells in the bovine placenta during the postpartum period and to compare these cells between normal and retained placenta. Within 1 h after normal calving, biopsy samples of placentomes were collected from 10 cows. The occurrence of retention of fetal membranes was monitored for more than 8 h post-calving, and the samples obtained were divided into two groups: normally discharged and retained placenta (n = 5 each). Immunohistochemical procedures were utilized to detect macrophages and T lymphocytes. Numerous CD14-positive macrophages were found in the stroma of both normal placenta and retained placenta whereas only a few CD3-positive T lymphocytes were found in both cases. However, histochemical staining for acid phosphatase, a predominant lysozomal enzyme, revealed that almost all macrophages showed strong enzyme activity in the normally discharged placentas, whereas in retained placenta the activity of acid phosphatase was conspicuously decreased in intensity. These results indicate that there are functional differences in placental macrophages between normal and retained placenta. 相似文献
998.
The majority of off-type plants in indica hybrid rice were CMS and its maintainer lines. 相似文献
999.
E. Skibild K. Dahlgaard Y. Rajpurohit B. F. Smith U. Giger 《The Journal of small animal practice》2001,42(6):298-300
Phosphofructokinase (PFK) deficiency is an autosomal recessive inherited disorder in dogs causing haemolytic crises and exertional myopathy. The clinical signs may be confused with those of recurrent immune-mediated haemolytic anaemia. The deficiency has been commonly observed in field trial (working) English springer spaniels (ESSPs), but also in the conformation line of ESSPs in the USA over the past two decades. This report documents the first family of ESSPs found with PFK deficiency in Europe. Two related adult ESSPs in Denmark had intermittent signs of pigmenturia after exercise (hunting) and had evidence of a regenerative haemolytic anaemia. Based upon DNA sequencing data, both dogs had the previously described nonsense point mutation in the muscle-type PFK gene (delta2228G-->A). Study of 17 related family members using a simple and accurate PFK-DNA test revealed one additional PFK-deficient dog (with minor exercise intolerance), nine carriers and seven normal (or 'clear') ESSPs. Recently, the authors have also identified PFK carriers and affected ESSPs in the UK. Screening for PFK deficiency is recommended for ESSPs with suspicious clinical signs and before using any for field trials or breeding in order to prevent the further spread of this hereditary disorder. 相似文献
1000.
霉菌毒素与免疫系统 总被引:1,自引:0,他引:1
某些霉菌毒素对肉鸡免疫系统的影响要比预想的更为严重。密苏里大学的一个研究小组通过在小鸡的饲料中添加不同水平的黄曲霉毒素 B1对此进行了研究。试验结果表明 ,在添加剂量为 2 0 0 μg/kg时 ,注射 E.Coli以及在饲料中添加黄曲霉毒素 B1组肝脏和脾脏中的细菌数比只注射 E.Coli组多。试验鸡在连续饲喂含黄曲霉毒素的饲料 4周后对新城疫灭活疫苗的应答较弱。和未添加组相比 ,添加组免疫细胞对毒素的应答较慢。小剂量添加时 ,没有发现免疫系统明显的损伤 ,由此表明 ,大剂量接触黄曲霉毒素可能会引起免疫系统明显的损伤霉菌毒素与免疫系统… 相似文献