全文获取类型
收费全文 | 15187篇 |
免费 | 980篇 |
国内免费 | 450篇 |
专业分类
林业 | 1662篇 |
农学 | 996篇 |
基础科学 | 364篇 |
3282篇 | |
综合类 | 1814篇 |
农作物 | 674篇 |
水产渔业 | 934篇 |
畜牧兽医 | 5122篇 |
园艺 | 418篇 |
植物保护 | 1351篇 |
出版年
2024年 | 27篇 |
2023年 | 127篇 |
2022年 | 217篇 |
2021年 | 369篇 |
2020年 | 337篇 |
2019年 | 264篇 |
2018年 | 628篇 |
2017年 | 652篇 |
2016年 | 596篇 |
2015年 | 521篇 |
2014年 | 576篇 |
2013年 | 824篇 |
2012年 | 1164篇 |
2011年 | 1057篇 |
2010年 | 682篇 |
2009年 | 573篇 |
2008年 | 883篇 |
2007年 | 853篇 |
2006年 | 744篇 |
2005年 | 772篇 |
2004年 | 596篇 |
2003年 | 538篇 |
2002年 | 467篇 |
2001年 | 352篇 |
2000年 | 345篇 |
1999年 | 354篇 |
1998年 | 197篇 |
1997年 | 153篇 |
1996年 | 128篇 |
1995年 | 149篇 |
1994年 | 106篇 |
1993年 | 115篇 |
1992年 | 142篇 |
1991年 | 115篇 |
1990年 | 122篇 |
1989年 | 91篇 |
1988年 | 79篇 |
1987年 | 68篇 |
1986年 | 61篇 |
1985年 | 49篇 |
1984年 | 48篇 |
1983年 | 42篇 |
1981年 | 27篇 |
1979年 | 39篇 |
1974年 | 26篇 |
1972年 | 24篇 |
1971年 | 23篇 |
1970年 | 27篇 |
1969年 | 26篇 |
1968年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
131.
132.
Gesto M Tintos A Alvarez R Soengas JL Míguez JM 《Fish physiology and biochemistry》2009,35(3):453-465
The contents of dopamine (DA), noradrenaline (NA), serotonin (5HT), and some related metabolites were studied in different
brain regions of rainbow trout at two different stages of sexual maturation (at the beginning of vitellogenesis), after naphthalene
(NAP) administration. The effects of NAP varied according to duration of exposure, brain region and vitellogenesis stage of
the trout, and were more significant during previtellogenesis. The changes observed in DA metabolism were generally stimulatory
after exposure for 3 h, and either stimulatory or inhibitory (depending on the brain regions) after exposure for 3 days to
NAP. NA levels were altered by NAP in various brain regions, but only during previtellogenesis. With respect to 5HT, treatment
with NAP reduced levels of the amine and/or its main metabolite in most of the brain regions studied, particularly 3 h after
treatment. The results suggest that NAP might interfere with the processes regulating brain monoamine metabolism, either locally
or indirectly by altering steroid feedback to brain centres, and thus disrupt endocrine control of reproductive development
through the brain–pituitary axis. 相似文献
133.
Luiz Henrique Agra Cavalcante-Silva Ana Carolina de Carvalho Correia José Maria Barbosa-Filho Bagnólia Araújo da Silva Bárbara Viviana de Oliveira Santos Daysianne Pereira de Lira Jéssica Celestino Ferreira Sousa George Emmanuel C. de Miranda Fabiana de Andrade Cavalcante Magna Suzana Alexandre-Moreira 《Marine drugs》2013,11(5):1553-1564
In this work, we investigated the spasmolytic effect of caulerpine, a bisindole alkaloid isolated from marine algae of the Caulerpa genus, on guinea pig ileum. Our findings indicated that caulerpine inhibited phasic contractions induced by carbachol (IC50 = 7.0 ± 1.9 × 10−5 M), histamine (IC50 = 1.3 ± 0.3 × 10−4 M) and serotonin (IC50 = 8.0 ± 1.4 × 10−5 M) in a non-selective manner. Furthermore, caulerpine concentration-dependently inhibited serotonin-induced cumulative contractions (pD′2 = 4.48 ± 0.08), shifting the curves to the right with Emax reduction and slope of 2.44 ± 0.21, suggesting a noncompetitive antagonism pseudo-irreversible. The alkaloid also relaxed the ileum pre-contracted by KCl (EC50 = 9.0 ± 0.9 × 10−5 M) and carbachol (EC50 = 4.6 ± 0.7 × 10−5 M) in a concentration-dependent manner. This effect was probably due to inhibition of Ca2+ influx through voltage-gated calcium channels (CaV), since caulerpine slightly inhibited the CaCl2-induced contractions in depolarizing medium without Ca2+, shifting the curves to the right and with Emax reduction. According to these results, the spasmolytic effect of caulerpine on guinea pig ileum seems to involve inhibition of Ca2+ influx through CaV. However, other mechanisms are not discarded. 相似文献
134.
Forterre F Konar M Tomek A Doherr M Howard J Spreng D Vandevelde M Jaggy A 《Journal of the American Veterinary Medical Association》2008,232(4):559-563
OBJECTIVE: To evaluate the accuracy of neurologic examination versus magnetic resonance imaging (MRI) in localization of cervical disk herniation and evaluate the usefulness of withdrawal reflex testing in dogs. DESIGN: Retrospective case series. ANIMALS: 35 client-owned dogs with a single-level cervical disk herniation as determined via MRI. PROCEDURES: 1 of 2 board-certified neurologists performed a complete neurologic examination in each dog. Clinical signs of a cervical lesion included evidence of neck pain and tetraparesis. The withdrawal reflex was used for neuroanatomic localization (C1-C5 or C6-T2). Agreement between results of neurologic and MRI examinations was determined. RESULTS: Agreement between neurologic and MRI diagnoses was 65.8%. In 11 dogs in which the lesion was clinically localized to the C6-T2 segment on the basis of a decreased withdrawal reflex in the forelimbs, MRI revealed an isolated C1-C5 disk lesion. In 1 dog, in which the lesion was suspected to be at the C1-C5 level, MRI revealed a C6-T2 lesion. Cranial cervical lesions were significantly associated with an incorrect neurologic diagnosis regarding site of the lesion. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that the withdrawal reflex in dogs with cervical disk herniation is not reliable for determining the affected site and that a decreased withdrawal reflex does not always indicate a lesion from C6 to T2. 相似文献
135.
在现场调研和文献资料查阅的基础上,分析行道树遮挡交通标志的问题及原因,从交通标志设置、行道树设置及部门机制等方面提出相关的改善对策。
相似文献
136.
137.
Miguel Mellado Lucía M. Treviño María I. Chavez Francisco G. Véliz Ulises Macías-Cruz Leonel Avendaño-Reyes José E. García 《Reproduction in domestic animals》2023,58(1):39-47
The objective of this retrospective study was to assess the effect of receiving a single (n = 50,285) or double (n = 4392) artificial insemination (AI), 12 h apart, within a timed artificial insemination protocol on pregnancy per AI (P/AI) in nulliparous heifers (inseminated with either sex-sorted or conventional semen) and pluriparous Holstein cows in a commercial dairy herd. Also, this study aimed to investigate the relationship between temperature-humidity index (THI) and time of the first AI and fertility. Fertility of cows receiving two AI with normothermia (THI <68) was higher (p < .05) than cows receiving a single AI (42.9% vs. 36.4%). P/AI of cows receiving two AI with severe heat stress (THI >85) was higher (p < .05) than cows receiving a single AI (21.0% vs. 12.6%). Regardless of heat stress conditions, applying the first AI in the morning increased (p < .05) P/AI in cows with double AI than in cows whose first AI occurred in the afternoon (38.4 vs. 33.3%). With moderate heat stress, and sexed-sorted semen, P/AI to timed AI was higher (65.0 vs. 51.9%; p < .05) in heifers receiving double AI than those serviced once. It was concluded that double AI, 12 h apart, enhanced fertility at timed AI than herd mates with a single AI, particularly with heat stress at breeding. 相似文献
138.
Twelve multiparous, cycling, lactating Holstein-Friesian cows were synchronised with prostaglandin F(2alpha) and treated with either 2.5 mg carazolol or saline. There were no differences between the peripheral blood concentrations of oestradiol or progesterone, but in the cows treated with carazolol the periovulatory surge of luteinising hormone was delayed, and oestrous behaviour was expressed later than in the control cows. 相似文献
139.
Durocher-Granger Léna Mfune Tibonge Musesha Monde Lowry Alyssa Reynolds Kathryn Buddie Alan Cafà Giovanni Offord Lisa Chipabika Gilson Dicke Marcel Kenis Marc 《Journal of pest science》2021,94(4):1133-1146
Journal of Pest Science - Invasive alien species have environmental, economic and social impacts, disproportionally threatening livelihood and food security of smallholder farmers in low- and... 相似文献
140.
Chantal?Le Marié Norbert?Kirchgessner Patrick?Flütsch Johannes?Pfeifer Achim?Walter Andreas?HundEmail author 《Plant methods》2016,12(1):40