全文获取类型
收费全文 | 3249篇 |
免费 | 222篇 |
国内免费 | 1篇 |
出版年
2023年 | 14篇 |
2022年 | 7篇 |
2021年 | 71篇 |
2020年 | 27篇 |
2019年 | 52篇 |
2018年 | 37篇 |
2017年 | 43篇 |
2016年 | 64篇 |
2015年 | 147篇 |
2014年 | 169篇 |
2013年 | 213篇 |
2012年 | 245篇 |
2011年 | 242篇 |
2010年 | 168篇 |
2009年 | 141篇 |
2008年 | 192篇 |
2007年 | 232篇 |
2006年 | 206篇 |
2005年 | 173篇 |
2004年 | 188篇 |
2003年 | 163篇 |
2002年 | 138篇 |
2001年 | 30篇 |
2000年 | 33篇 |
1999年 | 31篇 |
1998年 | 26篇 |
1997年 | 29篇 |
1996年 | 13篇 |
1995年 | 21篇 |
1994年 | 20篇 |
1993年 | 15篇 |
1992年 | 32篇 |
1991年 | 22篇 |
1990年 | 25篇 |
1989年 | 14篇 |
1988年 | 14篇 |
1987年 | 13篇 |
1986年 | 13篇 |
1985年 | 12篇 |
1984年 | 16篇 |
1983年 | 11篇 |
1982年 | 26篇 |
1981年 | 19篇 |
1980年 | 17篇 |
1979年 | 13篇 |
1978年 | 8篇 |
1976年 | 5篇 |
1975年 | 6篇 |
1974年 | 6篇 |
1970年 | 5篇 |
排序方式: 共有3472条查询结果,搜索用时 406 毫秒
1.
2.
Asymptotic distributions of kappa statistics and their differences with many raters,many rating categories and two conditions 下载免费PDF全文
Luca Grassano Guido Pagana Marco Daperno Enrico Bibbona Mauro Gasparini 《Biometrical journal. Biometrische Zeitschrift》2018,60(1):146-154
In clinical research and in more general classification problems, a frequent concern is the reliability of a rating system. In the absence of a gold standard, agreement may be considered as an indication of reliability. When dealing with categorical data, the well‐known kappa statistic is often used to measure agreement. The aim of this paper is to obtain a theoretical result about the asymptotic distribution of the kappa statistic with multiple items, multiple raters, multiple conditions, and multiple rating categories (more than two), based on recent work. The result settles a long lasting quest for the asymptotic variance of the kappa statistic in this situation and allows for the construction of asymptotic confidence intervals. A recent application to clinical endoscopy and to the diagnosis of inflammatory bowel diseases (IBDs) is shortly presented to complement the theoretical perspective. 相似文献
3.
Daniela Giordano Roberta Russo Daniela Coppola Giovanna Altomonte Guido di Prisco Stefano Bruno Cinzia Verde 《Hydrobiologia》2015,761(1):293-312
Notothenioidei, the taxonomic group of teleosts that dominates the Southern Ocean and dwell in the Ross Sea at large, provide an example of marine species that underwent unique adaptations to life at low temperatures and high oxygen concentrations, resulting in morphological, physiological, genomic, and biochemical peculiarities in comparison with warm-water fish. Global Warming raises concerns over the fate of these stenothermal fish, as their adaptation has been accompanied by irreversible genomic losses, which suggest a poor genetic potential to adapt to warmer climates. Specifically, this review focuses on adaptation of proteins belonging to the globin superfamily, which include the respiratory proteins hemoglobin and myoglobin and the non-respiratory proteins neuroglobin and cytoglobin. Here, we describe their molecular adaptations to cold temperatures in the framework of the physiology of oxygen transport and management of oxidative stress in fish species largely populating the Ross Sea. 相似文献
4.
Liliana Gianfreda Anna Maria Livolsi Maria Rosaria Scarfì Guido Greco 《Enzyme and microbial technology》1982,4(5):322-326
Cellobiose hydrolysis by β-d-glucosidase (β-d-glucoside glucohydrolase EC 3.2.1.21) can become the rate-limiting step in the hydrolysis of cellulosic wastes because of inhibition phenomena involving other enzymes of the cellulase complex. Enhancement of the overall rate can therefore be obtained by increasing the amount of β-d-glucosidase present in the reactor. Unfortunately, the thermal stability of β-d-glucosidase is rather poor compared to and cellobiohydrolase. A novel stabilization method is proposed that exploits the polarization phenomena that take place in an unstirred ultrafiltration membrane enzymatic reactor. As much as a 20-fold increase in half-life compared to the native enzyme is obtained by injecting small amounts of hydroxyethyl cellulose into the system. No reduction in enzyme activity levels is observed. 相似文献
5.
6.
7.
T. E. Graedel Julian Allwood Jean‐Pierre Birat Matthias Buchert Christian Hagelüken Barbara K. Reck Scott F. Sibley Guido Sonnemann 《Journal of Industrial Ecology》2011,15(3):355-366
The recycling of metals is widely viewed as a fruitful sustainability strategy, but little information is available on the degree to which recycling is actually taking place. This article provides an overview on the current knowledge of recycling rates for 60 metals. We propose various recycling metrics, discuss relevant aspects of recycling processes, and present current estimates on global end‐of‐life recycling rates (EOL‐RR; i.e., the percentage of a metal in discards that is actually recycled), recycled content (RC), and old scrap ratios (OSRs; i.e., the share of old scrap in the total scrap flow). Because of increases in metal use over time and long metal in‐use lifetimes, many RC values are low and will remain so for the foreseeable future. Because of relatively low efficiencies in the collection and processing of most discarded products, inherent limitations in recycling processes, and the fact that primary material is often relatively abundant and low‐cost (which thereby keeps down the price of scrap), many EOL‐RRs are very low: Only for 18 metals (silver, aluminum, gold, cobalt, chromium, copper, iron, manganese, niobium, nickel, lead, palladium, platinum, rhenium, rhodium, tin, titanium, and zinc) is the EOL‐RR above 50% at present. Only for niobium, lead, and ruthenium is the RC above 50%, although 16 metals are in the 25% to 50% range. Thirteen metals have an OSR greater than 50%. These estimates may be used in considerations of whether recycling efficiencies can be improved; which metric could best encourage improved effectiveness in recycling; and an improved understanding of the dependence of recycling on economics, technology, and other factors. 相似文献
8.
Sandrine Poncet Armelle Delecluse Guido Anello ré Klier Georges Rapoport 《FEMS microbiology letters》1994,117(1):91-95
Abstract The genes encoding the CryIVB and CryIVD crystal polypeptides of B. thuringiensis subsp. israelensis were cloned indepently on a stable shuttle vector, and transfered into B. sphaericus 2297. Recombinant cells expressed the B. thuringiensis toxins during sporulation and were shown to be toxic to Aedes aegypti fourth instar larvae, whereas the parental strain was not. 相似文献
9.
10.