全文获取类型
收费全文 | 5330篇 |
免费 | 448篇 |
国内免费 | 1篇 |
出版年
2023年 | 23篇 |
2022年 | 57篇 |
2021年 | 140篇 |
2020年 | 78篇 |
2019年 | 97篇 |
2018年 | 144篇 |
2017年 | 111篇 |
2016年 | 190篇 |
2015年 | 270篇 |
2014年 | 286篇 |
2013年 | 397篇 |
2012年 | 444篇 |
2011年 | 490篇 |
2010年 | 299篇 |
2009年 | 260篇 |
2008年 | 312篇 |
2007年 | 354篇 |
2006年 | 297篇 |
2005年 | 263篇 |
2004年 | 267篇 |
2003年 | 248篇 |
2002年 | 202篇 |
2001年 | 46篇 |
2000年 | 37篇 |
1999年 | 44篇 |
1998年 | 55篇 |
1997年 | 42篇 |
1996年 | 44篇 |
1995年 | 33篇 |
1994年 | 23篇 |
1993年 | 19篇 |
1992年 | 21篇 |
1991年 | 20篇 |
1990年 | 22篇 |
1989年 | 14篇 |
1988年 | 12篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 7篇 |
1984年 | 7篇 |
1983年 | 9篇 |
1982年 | 8篇 |
1981年 | 9篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1976年 | 5篇 |
1973年 | 5篇 |
1971年 | 6篇 |
1935年 | 4篇 |
排序方式: 共有5779条查询结果,搜索用时 281 毫秒
41.
Davide Scaccini Davide Bramuzzo Cengiz Bostancı Massimo Faccoli Isabel Martinez-Sañudo Alexey Matov Alberto Zilli Alberto Pozzebon 《Journal of Applied Entomology》2023,147(3):239-243
The Asian walnut moth, Garella musculana (Erschov, 1874) (Lepidoptera: Nolidae), is a major pest of walnut. Native to Central Asia, it was found to be invasive in 2008 in Sevastopol (Crimea) and nowadays widespread in Turkey, Bulgaria, Romania and Russia. Here, we account for the finding of G. musculana in NE Italy (Veneto region) in 2021, where adults were found in a light lamp, representing the first record of the Asian walnut moth for this country and Western Europe. Adult specimens were identified morphologically on both external characters and genitalia features. G. musculana larvae and damage were also observed on a plantation of Juglans regia L. (Fagales: Juglandaceae) located in Veneto in October 2021. A COI-barcoding analysis was performed to attain a molecular characterization of our specimens and probate our morphological identification. However, because no sequence of G. musculana was present in major gene databases and the similarity of our sequences with those attributed to Garella ruficirra (Hampson, 1905) (Lepidoptera: Nolidae) made clear that these taxa deserved further scrutiny regarding their specific distinction. Some subtle differences in the male terminalia could be found between them and their vast geographic distributions, but the strong similarity in most features calls for further morphological and genetical insights on a broad set of samples to assess whether they represent two closely related, substantially parapatric species, or a unique, geographically varying entity. Solving this issue may turn out crucial in the identification and proper management of walnut moths of the genus Garella. 相似文献
42.
Ysabel Santos R. Laixier Isabel Bandin J. Lamas Alicia E. Toranzo 《Zeitschrift fur angewandte Ichthyologie》1991,7(3):160-167
The susceptibility of turbot, coho salmon, and rainbow trout to strains of Vibrio anguillarum of serotypes 01 and 02 and their extracellular products (ECP) was investigated in order to clarify the role of exotoxins in the mechanism of virulence of both serotypes. All V. anguillarum isolates were virulent for trout, salmon, and turbot. Despite the origin of the strains tested, rainbow trout was the most susceptible fish species to experimentally induced vibriosis. Coho salmon and turbot did not differ significantly in their susceptibility to V. anguillarum live cells. In contrast, the ECP from Vibrio strains of serotypes 01 and 02 exhibited similar lethal dose for turbot, salmon, and trout (ranging from 4.52 to 7.32 μg protein/g fish). Therefore, differences in susceptibility to vibriosis are not completely due to a differential sensitivity of fish to the extracellular products of Vibrio strains. The ECP from 7 of 10 V. anguillarum strains possessed vascular permeability factors, and all the extracts displayed proteolytic, hemolytic and cytotoxic activities. All the biological activities of ECP were lost after heat treatment at 80° C/10 min. 相似文献
43.
Aonio Bernao Isabel Meseguer María Victorina Aguilar María Carmen Martínez Para María José González Mu?oz 《Journal of trace elements in medicine and biology》2004,18(1):33-39
This 12-day study was conducted to evaluate the effects of three different levels of dietary chromium (100, 200, and 500 microg/day) in the form of chromium picolinate (CrPic) on growth and protein use in weaned rats. No significant effect of CrPic on body weight gain, food intake, or food conversion rate was observed. Elevated doses of CrPic seemed to increase muscle mass, either by stimulating protein anabolism by activation of insulin by chromium or by lowering protein degradation. However, these effects had no repercussions on overall growth, suggesting that any anabolic effect of chromium due to the action of insulin was probably marginal. 相似文献
44.
Isabel Figueiral 《Vegetation History and Archaeobotany》1996,5(1-2):121-129
The analysis of archaeological charcoal is used to reconstruct the wood resources in north-west Portugal from the late Bronze
Age to the Roman period. In this paper, the results obtained from 12 sites are considered, and their implications for interpreting
historical human behaviour towards the natural environment and vegetation are discussed. The results indicate a similar kind
of exploitation of the vegetation by different populations which used a similar range of wood resources. Fifty-one taxa are
identified and three main natural biotopes are distinguished, including mixed oak forest, wasteland vegetation and riparian
forest. The large number of taxa identified seems to testify to the existence of a good sampling of the woody vegetation growing
in the proximity of the settlements. Both dry and fresh wood were used, and the value and possible uses are suggested for
some of the most frequent taxa identified. 相似文献
45.
Howard J. Williams Isabel Sattler Guillermo Moyna A. Ian Scott Alois A. Bell S. Bradleigh Vinson 《Phytochemistry》1995,40(6):1633-1636
Major sesquiterpene components of oil of Texas Race Stock 810 of Gossypium hirsutum were - and β-selinene. This is the seventh cyclic terpene type found to date in this genus. Both - and β-selinene, along with aromadendrene, were found but only as minor components of extracts of several domestic cultivars of G. hirsutum. 相似文献
46.
47.
The effect of heating and autoclaving on extractable nitrogen, N mineralisation and C metabolism was studied by heating five forest soils in the laboratory, simulating the range of effects of heat due to bushfire. Top soil (0–5 cm) was heated to 60 °C, 120 °C and 250 °C for 30 minutes; unheated soil was taken as a control. Samples of the soil heated to 250 °C were also inoculated with fresh soil to accelerate the recovery of the microbial population. Soil autoclaving was carried out as another heat treatment (moist heat). Soils were analysed immediately after heating and 3 times during seven months of incubation to assess immediate and longer-term effects of heating.Extractable N (organic and mineral forms) increased after heating to 120 °C, but decreased with further heating to 250 °C suggesting the volatilisation of N. N associated with microbial biomass diminished with heating and was barely detectable after the 250 °C treatment. Microbial biomass was an important source of soluble N in heated soils, and only partly recovered during subsequent long incubation. The amount of N mineralised during incubation depended on both soil and temperature. Nitrification did not occur when soils were heated to 250 °C (with or without inoculum), or after autoclaving, demonstrating the high sensitivity of nitrifiers to heat. At the beginning of soil incubation, respiration was enhanced in heated soils (250 °C, 250 °C inoculated) and autoclaved soils, but after 30 days of incubation respiration decreased to values either similar to or lower than those in control. This respiration pattern indicated that a fraction of labile C was released by heating, which was quickly mineralised within 30 days of incubation. These results demonstrate some effects of soil heating on C and N dynamics in forest soils. 相似文献
48.
49.
50.
Vera Gamulin Alexander Skorokhod Vadim Kavsan Isabel M. Müller Werner E. G. Müller 《Journal of molecular evolution》1997,44(3):242-252
We have analyzed the gene that encodes receptor tyrosine kinase (RTK) from the marine sponge Geodia cydonium, which belongs to the most ancient and simple metazoan groups, the Porifera. RTKs are enzymes found only in metazoa. The sponge
gene contains two introns in the extracellular part of the protein. However, the rest of the protein (transmembrane and intracellular
part), including the tyrosine kinase (TK)-domain, is encoded by a single exon. In contrast, all TK genes, so far known only
from higher animals (vertebrates), contain several introns especially in the TK-domain. The TK-domain of G. cydonium shows similarity with numerous members of receptor as well as nonreceptor TKs. Phylogenetic analysis of the sponge TK-domain
indicates that this enzyme branched off first from the common tree of metazoan TK proteins. Consequently, we assume that introns,
found in the TK-domains of genes from higher animals, were inserted into these genes after splitting off the sponge taxa from
other metazoan organisms (over 600 million years ago). Our results support the view that ancient genes were not ``in pieces.'
Received: 8 August 1996 / Accepted: 4 November 1996 相似文献