全文获取类型
收费全文 | 20555篇 |
免费 | 1660篇 |
国内免费 | 11篇 |
出版年
2023年 | 64篇 |
2022年 | 47篇 |
2021年 | 310篇 |
2020年 | 226篇 |
2019年 | 322篇 |
2018年 | 379篇 |
2017年 | 349篇 |
2016年 | 556篇 |
2015年 | 949篇 |
2014年 | 1073篇 |
2013年 | 1345篇 |
2012年 | 1564篇 |
2011年 | 1461篇 |
2010年 | 955篇 |
2009年 | 882篇 |
2008年 | 1142篇 |
2007年 | 1086篇 |
2006年 | 1099篇 |
2005年 | 1061篇 |
2004年 | 999篇 |
2003年 | 873篇 |
2002年 | 923篇 |
2001年 | 273篇 |
2000年 | 228篇 |
1999年 | 244篇 |
1998年 | 262篇 |
1997年 | 195篇 |
1996年 | 207篇 |
1995年 | 206篇 |
1994年 | 221篇 |
1993年 | 211篇 |
1992年 | 196篇 |
1991年 | 153篇 |
1990年 | 125篇 |
1989年 | 144篇 |
1988年 | 141篇 |
1987年 | 101篇 |
1986年 | 103篇 |
1985年 | 123篇 |
1984年 | 142篇 |
1983年 | 107篇 |
1982年 | 133篇 |
1981年 | 108篇 |
1980年 | 107篇 |
1979年 | 93篇 |
1978年 | 90篇 |
1977年 | 81篇 |
1976年 | 53篇 |
1974年 | 54篇 |
1973年 | 67篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
93.
The urea concentration in the renal cortex ([RC]), liver ([L]) and skeletal muscle ([SM]) of non-diuretic Wistar rats was measured chemically and after an i.m. injection of 14C-urea and was compared with the plasma urea concentration ([P]). [L]/[P] and [SM]/[P] always equalled 1, irrespective of whether they were measured chemically or by means of radioactivity. [RC]/[P] was 2.81, again without any difference between chemical and radioactive measurement. The ratio of the chemically measured urea concentration in the renal cortex and plasma of mongrel dogs was 5.71, i.e. significantly higher than in rats (p less than 0.01). The intrarenal infusion of KCN, iodoacetate and ouabain did not alter it significantly (5.52, p greater than 0.05). Active transport, in whatever form, does not seem to be the cause of the high urea concentration in rat and dog renal cortex. 相似文献
94.
Maree L Hackett Nicholas S Glozier Alexandra L Martiniuk Stephen Jan Craig S Anderson 《BMC neurology》2011,11(1):3
Background
Epilepsy affects an estimated 50 million people and accounts for approximately 1% of days lost to ill health globally, making it one of the most common, serious neurological disorders. While there are abundant global data on epilepsy incidence, prevalence and treatment, there is a paucity of Australian incidence data. There is also a general lack of information on the psychosocial impact and socioeconomic consequences of a new diagnosis of epilepsy on an individual, their family, household, and community which are often specific to the health and social system of each country. 相似文献95.
96.
Jan Suchá?ek Petr Sed’a Václav Friedrich Renata Wachowiak-Smolíková Mark P. Wachowiak 《PloS one》2016,11(11)
Media, and particularly TV media, have a great impact on the general public. In recent years, spatial patterns of information and the relevance of intangible geographies have become increasingly important. Gatekeeping plays a critical role in the selection of information that is transformed into media. Therefore, gatekeeping, through national media, also co-forms the generation of mental maps. In this paper, correspondence analysis (a statistical method) combined with cloud lines (a new visual analytics technique) is used to analyze how individual major regional events in one of the post-communist countries, the Czech Republic, penetrate into the media on a national scale. Although national news should minimize distortions about regions, this assumption has not been verified by our research. Impressions presented by the media of selected regions that were markedly influenced by one or several events in those regions demonstrate that gatekeepers, especially news reporters, functioned as a filter by selecting only a few specific, and in many cases, unusual events for dissemination. 相似文献
97.
Routine neurological examination of patients one hour after cardiac arrest seems to be of value in determining the prognosis for life and likelihood of intellectual impairment.In 48 patients 53 episodes of cardiac arrest were followed by serial neurological examinations. Patients were divided into two groups according to neurological findings one hour after cardiac arrest. Patients in group 1 were unresponsive or at most responded in a reflex fashion to painful stimuli at one hour; these patients died or survived with intellectual damage. Patients in group 2 responded purposefully at one hour and survived without neurological damage. These patients commonly showed transient confusional states and a variety of other non-focal abnormalities, and focal signs were seen occasionally. 相似文献
98.
99.
Therese Pluess Vojtěch Jaro?ík Petr Py?ek Ray Cannon Jan Pergl Annemarie Breukers Sven Bacher 《PloS one》2012,7(10)
Although issues related to the management of invasive alien species are receiving increasing attention, little is known about which factors affect the likelihood of success of management measures. We applied two data mining techniques, classification trees and boosted trees, to identify factors that relate to the success of management campaigns aimed at eradicating invasive alien invertebrates, plants and plant pathogens. We assembled a dataset of 173 different eradication campaigns against 94 species worldwide, about a half of which (50.9%) were successful. Eradications in man-made habitats, greenhouses in particular, were more likely to succeed than those in (semi-)natural habitats. In man-made habitats the probability of success was generally high in Australasia, while in Europe and the Americas it was higher for local infestations that are easier to deal with, and for international campaigns that are likely to profit from cross-border cooperation. In (semi-) natural habitats, eradication campaigns were more likely to succeed for plants introduced as an ornamental and escaped from cultivation prior to invasion. Averaging out all other factors in boosted trees, pathogens, bacteria and viruses were most, and fungi the least likely to be eradicated; for plants and invertebrates the probability was intermediate. Our analysis indicates that initiating the campaign before the extent of infestation reaches the critical threshold, starting to eradicate within the first four years since the problem has been noticed, paying special attention to species introduced by the cultivation pathway, and applying sanitary measures can substantially increase the probability of eradication success. Our investigations also revealed that information on socioeconomic factors, which are often considered to be crucial for eradication success, is rarely available, and thus their relative importance cannot be evaluated. Future campaigns should carefully document socioeconomic factors to enable tests of their importance. 相似文献
100.