全文获取类型
收费全文 | 7738篇 |
免费 | 443篇 |
国内免费 | 3篇 |
专业分类
8184篇 |
出版年
2023年 | 19篇 |
2022年 | 63篇 |
2021年 | 105篇 |
2020年 | 56篇 |
2019年 | 87篇 |
2018年 | 100篇 |
2017年 | 111篇 |
2016年 | 145篇 |
2015年 | 260篇 |
2014年 | 301篇 |
2013年 | 532篇 |
2012年 | 478篇 |
2011年 | 476篇 |
2010年 | 353篇 |
2009年 | 307篇 |
2008年 | 527篇 |
2007年 | 510篇 |
2006年 | 520篇 |
2005年 | 500篇 |
2004年 | 495篇 |
2003年 | 485篇 |
2002年 | 475篇 |
2001年 | 72篇 |
2000年 | 69篇 |
1999年 | 113篇 |
1998年 | 109篇 |
1997年 | 83篇 |
1996年 | 74篇 |
1995年 | 62篇 |
1994年 | 81篇 |
1993年 | 68篇 |
1992年 | 65篇 |
1991年 | 52篇 |
1990年 | 27篇 |
1989年 | 29篇 |
1988年 | 39篇 |
1987年 | 27篇 |
1986年 | 29篇 |
1985年 | 28篇 |
1984年 | 34篇 |
1983年 | 18篇 |
1982年 | 29篇 |
1981年 | 28篇 |
1980年 | 16篇 |
1979年 | 26篇 |
1978年 | 13篇 |
1977年 | 18篇 |
1975年 | 11篇 |
1974年 | 9篇 |
1970年 | 7篇 |
排序方式: 共有8184条查询结果,搜索用时 0 毫秒
41.
Mitsumasa Haruna Makiko Kato Kazuo Ito Toshiaki Nikai Hisayoshi Sugihara Hiroyuki Muratat 《Phytochemistry》1981,20(11):2583-2584
Angeloylcumambrin-B, a new antimicrobial guaianolide sesquiterpene lactone, was isolated from Chrysanthemum ornatum and the structure was determined by a combination of chemical and physical methods. 相似文献
42.
Differences between surface antigenic determinants of polar monotrichous flagella of Vibrio parahaemolyticus and of related species 总被引:2,自引:0,他引:2
Polar monotrichous flagella (M-flagella) of Vibrio parahaemolyticus have antigens in common with those of various species of Vibrio including V. cholerae and V. anguillarum, and of Beneckea, revealed by gel diffusion tests with flagelli monomers. However, antiserum against M-flagellin of V. parahaemolyticus did not agglutinate cells of V. cholerae and V. anguillarum, although it did agglutinate cells of V. parahaemolyticus. Agglutination tests after absorption of the antiserum with purified M-flagellar filaments or flagellin monomers and H-agglutination inhibition tests demonstrated that there are two different antigenic determinants in M-flagella as in lateral flagella. One is on the surface of the M-flagella (surface antigenic determinant, SA) and disappears or is buried in dissociated monomers. The other is inside the flagella (internal antigenic determinant, IA) and is exposed when the flagella are dissociated to flagellin monomers. SA of V. parahaemolyticus is different from those of V. cholerae and V. anguillarum, whereas the three species have a common IA. 相似文献
43.
44.
M Kashiwazaki S Namioka K Mitani M Kono T Nakahara 《National Institute of Animal Health quarterly》1975,15(4):186-191
An effective and economical method was developed for procuring and rearing calves in gnotobiotic conditions. To evaluate apparatuses and surgical techniques, three calves, 1 to 3, welf 1 was weak and pale at delivery and died within 5 hours after delivery. Calf 2 was delivered alive, but died from a human error at 3 days of age. It was free from demonstrable bacteria and fungi at that time. Calf 3 was also successfully delivered and raised. It was killed at 10 days of age, since fungi were isolated from the feces and waste materials from it. 相似文献
45.
From leaves and twigs of Ixora chinensis, two new iridoid glucosides, ixoroside (1) and ixoside (7,8-dehydroforsythide) (2) along with known geniposidic acid (3) have been isolated and their structures have been established. 相似文献
46.
Yasuaki Yanagawa Rieko Shimogawara Misao Takano Takahiro Aoki Daisuke Mizushima Hiroyuki Gatanaga Yoshimi Kikuchi Shinichi Oka Kenji Yagita Koji Watanabe 《PLoS neglected tropical diseases》2022,16(4)
BackgroundAmebiasis, caused by Entamoeba histolytica, is spreading in developing countries and in many developed countries as a sexually transmitted infection. Here, we evaluated the efficacy of serological screening to identify asymptomatic E. histolytica infection as a potential epidemiological control measure to limit its spread.Methodology/Principal findingsThis cross-sectional study was carried out between January and March 2021 in an HIV-negative men who have sex with men (MSM) cohort at the National Center for Global Health and Medicine. Serological screening was performed using a commercially available ELISA kit. For seropositive individuals, we performed stool polymerase chain reaction (PCR) to determine current E. histolytica infection. We performed E. histolytica serological screening of 312 participants. None had a history of E. histolytica infection prior to the study. The overall E. histolytica seropositivity was 6.7% (21/312), which was similar to that found by the rapid plasma reagin test (17/312). We identified current infection in 8 of 20 seropositive participants (40.0%) by stool PCR.Conclusions/SignificanceOur serological screening approach constitutes a potentially practical epidemiological strategy. Active epidemiological surveys, in combination with an effective screening strategy for asymptomatically infected individuals, should be applied to help reduce sexually transmitted E. histolytica infections. 相似文献
47.
48.
Daisuke S. Yamamoto Megumi Sumitani Katsumi Kasashima Hideki Sezutsu Hiroyuki Matsuoka 《PLoS pathogens》2016,12(9)
Malaria is an important global public health challenge, and is transmitted by anopheline mosquitoes during blood feeding. Mosquito vector control is one of the most effective methods to control malaria, and population replacement with genetically engineered mosquitoes to block its transmission is expected to become a new vector control strategy. The salivary glands are an effective target tissue for the expression of molecules that kill or inactivate malaria parasites. Moreover, salivary gland cells express a large number of molecules that facilitate blood feeding and parasite transmission to hosts. In the present study, we adapted a functional deficiency system in specific tissues by inducing cell death using the mouse Bcl-2-associated X protein (Bax) to the Asian malaria vector mosquito, Anopheles stephensi. We applied this technique to salivary gland cells, and produced a transgenic strain containing extremely low amounts of saliva. Although probing times for feeding on mice were longer in transgenic mosquitoes than in wild-type mosquitoes, transgenic mosquitoes still successfully ingested blood. Transgenic mosquitoes also exhibited a significant reduction in oocyst formation in the midgut in a rodent malaria model. These results indicate that mosquito saliva plays an important role in malaria infection in the midgut of anopheline mosquitoes. The dysfunction in the salivary glands enabled the inhibition of malaria transmission from hosts to mosquito midguts. Therefore, salivary components have potential in the development of new drugs or genetically engineered mosquitoes for malaria control. 相似文献
49.
Ishibashi S Iwakiri R Shimoda R Ootani H Kawasaki S Tadano J Kikkawa A Ootani A Oda K Fujise T Yoshida T Tsunada S Sakata H Fujimoto K 《Helicobacter》2002,7(4):245-249
Background. Phospholipids concentration in the gastric mucosa decreased in patients with Helicobacter pylori infection. The aim of this study is to examine the effects of eradication of H. pylori on decreasing the phospholipids concentration in the gastric mucosa in patients with gastric or duodenal ulcer. Materials and Methods. Phospholipids (phosphatidylcholine, phosphatidylethanolamine, and sphingonomyeline) were measured in biopsy specimens from the antrum and corpus using thin‐layer chromatography. In H. pylori positive patients with gastric ulcer (n = 26) and duodenal ulcer (n = 13), and H. pylori negative controls (n = 20), the biopsy specimens were obtained before and 3 months after eradication. Eradication was performed using lansoprazole, amoxycillin, and clarithromycin. Results. Compared with the H. pylori negative control group, the concentrations of phosphatidylcholine and phosphatidylethanolamine decreased significantly in the gastric ulcer group in both antrum and corpus mucosa, and in the duodenal ulcer group in antrum mucosa. This decrease returned to the control level after eradication. Conclusions. This study demonstrates that the eradication of H. pylori in patients with peptic ulcer normalized the decrease of phosphatidylcholine and phosphatidylethanolamine in the gastric mucosa. 相似文献