全文获取类型
收费全文 | 1750篇 |
免费 | 104篇 |
国内免费 | 31篇 |
出版年
2023年 | 34篇 |
2022年 | 41篇 |
2021年 | 72篇 |
2020年 | 61篇 |
2019年 | 53篇 |
2018年 | 47篇 |
2017年 | 69篇 |
2016年 | 68篇 |
2015年 | 59篇 |
2014年 | 70篇 |
2013年 | 123篇 |
2012年 | 70篇 |
2011年 | 74篇 |
2010年 | 70篇 |
2009年 | 95篇 |
2008年 | 96篇 |
2007年 | 90篇 |
2006年 | 55篇 |
2005年 | 74篇 |
2004年 | 72篇 |
2003年 | 38篇 |
2002年 | 45篇 |
2001年 | 37篇 |
2000年 | 26篇 |
1999年 | 32篇 |
1998年 | 23篇 |
1997年 | 22篇 |
1996年 | 12篇 |
1995年 | 15篇 |
1994年 | 10篇 |
1993年 | 14篇 |
1992年 | 12篇 |
1991年 | 12篇 |
1989年 | 9篇 |
1988年 | 9篇 |
1987年 | 6篇 |
1986年 | 14篇 |
1985年 | 13篇 |
1984年 | 17篇 |
1983年 | 10篇 |
1982年 | 19篇 |
1981年 | 14篇 |
1980年 | 15篇 |
1979年 | 11篇 |
1978年 | 11篇 |
1977年 | 10篇 |
1976年 | 12篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1973年 | 8篇 |
排序方式: 共有1885条查询结果,搜索用时 15 毫秒
1.
J. L. Wilkens T. Kuramoto 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1998,168(7):483-490
The decapod cardiovascular system consists of a single ventricle that pumps blood into seven arteries; previous work has
shown that the outflow distribution patterns of intact animals are variable. In the present study, flow recordings were made
from pairs of arteries in semi-isolated hearts whilst different cardioactive hormones were infused into the heart. Each hormone
(5-hydroxytryptamine, octopamine, dopamine, proctolin and F1) changed the outflow pattern, heart rate and ventricular pressure
in a unique way. The probable sites of hormone action are the cardioarterial valves located at the origin of each artery except
one, the dorsal abdominal. Outflow from the dorsal abdominal is controlled downstream by valves located at the origin of the
segmental lateral arteries. The responses to a particular hormone were sometimes different between the hearts of American
and Japanese lobsters.
Accepted: 11 May 1998 相似文献
2.
Jerome Goddard 《Journal of vector ecology》2009,34(2):238-242
Rickettsia parkeri, a member of the spotted fever group rickettsias, was first described in 1939 and was thought to be non‐pathogenic until recently, when it was found to cause a spotted fever‐like illness in humans and areas of necrosis (eschars) at the sites of tick bites. Accordingly, there is currently much interest in this emerging pathogen. In this study, all published articles concerning R. parkeri were reviewed and analyzed for evidence of relatedness among this agent and other spotted fever group (SFG) rickettsiae which also produce similar clinical syndromes and/or eschars, including R. conorii, R. africae, and R. sibirica. A synthesis of the historical (antigenic) and recent (molecular) data supporting a phylogenetic sub‐grouping of these SFG organisms is presented and comments are offered about the taxonomy of rickettsial organisms in general, and R. parkeri in particular. 相似文献
3.
4.
The present study is an attempt to investigate the presence of Naegleria fowleri in Indian population. A total of 307 patients were enrolled and water samples were collected from both residential and surrounding areas of patients found positive for N. fowleri. The different species of Naegleria from both clinical and water samples were identified taxonomically. Recommended microbiological conventional techniques were used to identify different Naegleria stages and other free-living amoebae from the samples. PCR assays, using both genus and species specific primers were also optimized. None of the samples were positive by conventional microbiological examinations. However, PCR assays detected only three samples positive for N. fowleri. A total of 10 water bodies (ponds), that were used by Naegleria positive patients were examined. The pH and temperature of the water samples collected from water bodies ranged between 5.6–7.2 and 25–32 °C respectively. Among all the 10 water samples tested, four samples were positive for genus Naegleria by PCR assay, of which only two samples, showed positive amplification for N. fowleri. The sequence analysis of N. fowleri strain belonged to genotype II. 相似文献
5.
MORGAN PERKINS 《American anthropologist》2004,106(3):595-599
This review essay of Across Borders: Beadwork in Iroquois Life focuses on the display of beadwork as a cultural practice that has evolved significantly throughout its history while remaining central to Iroquois identity. The exhibition draws on historical documentation, objects, and imagery that depict the varied uses of beadwork as ritual objects, sources of income, markers of identity, and as works of art. The content and narrative for the display was developed through a broad collaboration between curators, scholars, artists, and members of two Iroquois communities. The changing and continued importance of beadwork is reflected in the adaptation of materials and styles for different forms of production and use. Across Borders places Iroquois beadwork in a broad context while concentrating on specific forms and meanings that are attached to beadwork, whether created in community gatherings or by individual artists. 相似文献
6.
L. L. WALLACE 《The New phytologist》1987,105(4):619-632
7.
Ten species of Lepadella Bory de St. Vincent, 1826, including one new species and one new form, are documented from North-Eastern India. Two of these species are new records from this country and six are new reports from N.E. region. Comments are also made on the status and distribution of various Indian taxa. 相似文献
8.
Mehmet Yaar can 《American journal of physical anthropology》1989,78(1):3-8
This study analyzes and compares the dental size variation and sexual dimorphism of the Highland Beach Mound people, a late southeastern prehistoric aboriginal Florida population (ca. 800-1200 AD) with a somewhat earlier midwestern group (ca. 200-800 AD) and an Archaic sample (ca. 4160-2558 BC). The lengths and breadths of maxillary and mandibular permanent teeth of 99 individuals were measured, and crown surface areas were calculated for the molars. Results indicated that there was little sexual dimorphism. Only the mesiodistal dimensions of the upper P2 and lower C were significantly different at the P less than 0.05 level. In terms of dental size, what appears to be a chronologically based reduction in most points of comparison was seen in all three groups, with the exception of the molars, which were larger in the Highland Beach sample than in the earlier Schultz Mound. 相似文献
9.
Tex A. Sordahl 《Evolutionary ecology》1988,2(3):189-196
Summary The body of theory concerning life-history strategies predicts that the duration of high-mortality stages should be minimized by natural selection. This is especially applicable to the avian pre-flight stage, during which growth rates typically are rapid. Using the American Avocet (Recurvirostra americana) as a paradigm, I propose a developmental strategy by which young animals can lower their mortality rates by an accelerated (and deceptive) acquisition of adult or adult-like characters. The benefit accrues when predators misidentify the vulnerable young as adults and fail to attack them because adults are much less vulnerable. This strategy, termed adult automimicry, is most likely to occur in precocial species living in open habitats.American Avocets are large, precocial, open-country shorebirds that first fly when about 4–5 weeks old. They develop a juvenal, plumage in their third week that resembles adult breeding plumage in pattern and color, even though plumage details are different. At this time chicks begin using adult foraging techniques and tend to move away rather than hide from potential predators. A few weeks later they acquire a first winter plumage that resembles adult winter plumage. Thus, avocet chicks appear unusually adult-like after their second week. This should make it difficult for distant predators to distinguish flightless chicks from volant adults. 相似文献
10.
K. C. Malhotra T. S. Vasulu Y. S. Dikshitulu R. C. Gupta 《International Journal of Anthropology》1992,7(1):23-40
An attempt was made to investigate dermatoglyphic variation between four sex-crimes (SC) and four sex and other crime (SOC) convicts. These were compared with 10 endogamous and 11 penal populations. The results indicate that the two closely related sex crime cases IPC-363 and IPC 366 («kidnap» and «abducting») show wide differences in dermatoglyphic characters. A comparison of sex crimes with sex and other crime cases showed least differences in the case of IPC-363, IPC-363 KC and in IPC 366 and IPC-366 AC but wide differences in IPC-354 («molestation») cases. The dendrograms suggest that the eight sex crime cases cluster together and are different from other endogamous and penal populations. The significant low mean finger ridge count observed in the case of IPC-366 is in agreement with other studies, suggesting a strong association between crime (sex) and dermatoglyphics. 相似文献